For me I pretty much brought all DnD 5e books via beyond so its all in one place, I DM using digital anyhow, my DM Screen my laptop and tablet which as the info I need up on screen. But its very much personal choice.

That's a decision for you. Some thoughts:

Pros:

1. You can carry all your content on a phone or tablet. No need to carry a library with you.
2. You can access it any time - suddenly have a few hours free that you didn't expect? Download it and go.
3. Updates and errata are automatic. No need to have post its with errata on.
4. You can use the character generator with your content. Automatic character sheets too.
5. Usually cheaper (for it's usually about £24 for a book here as opposed to £30 on Amazon). You can get bundles as well for further discounts.
6. You can buy piecemeal. So if a book is $30, you can buy just an option for $2. If you then want to buy the whole book, it will be only $28, so you've not paid any more for that option. I have to be fair, that's a really generous offer.
7. It makes it easier to play over the Internet, especially if you're using DDB as a medium.
8. You can have multiple copies (which should be for your own personal use, I feel must add).
9. Have a house fire or flood? No problem. When you get your new tablet you can download it again free of charge or hassle. Can't say the same for books.

Cons:

1. If anything happens to DDB's licence, you are screwed. WotC may or may not honour your arrangement with DDB, so you may well lose everything you've paid for.
2. If you don't like the errata and updates...that sucks, because you're getting them anyway.
3. If you lose access to your account and can't get it back, you're stuck.
4. Officially, it's in-app or in-browser only. You can't just put it on your e-reader or use it offline on your computer. There are ways, but it's still effort.
5. It's a screen, if that matters.

You have to decide what you prefer. Cons 1 & 3 are very unlikely be an issue, but you need to bear them in mind, that's a lot of money after all. The errata and updates are very important. Check up on the direction WotC are taking because otherwise you'll be very upset if they change or take way a feature that you like. 4 & 5 is a very personal taste thing. I prefer books to read, but that's up to you. I also like it on an e reader if it is a screen, so I don't like DDB content for those reasons. Also bear in mind that apart from the Essential Kit, you don't get content on DDB when you buy physical stuff. You never get physical d you buy on DDB. They're separate domains.

Since you are all new players, I highly recommend you use D&D Beyond. Character generation is complicated and figuring it out pen and paper without having someone experienced in the party to guide you can be a bit of a nightmare. Beyond that (pun not intended), the character sheets are user friendly and the encounter builder is a nifty tool for DMing.

If you decide to use D&D beyond, you next have to decide how to purchase content.  There are two main ways you can purchase content - each player purchase what they need for themselves, or one player purchases a Master level subscription, all the content the players need, and then shares the content. 

There are benefits to each, but, before I get into that, I want to address what is actually needed for the campaign. You do not need to buy everything to start, or really buy very much. 

For the players (to be purchased individually or, if sharing content, by the one person who is sharing for each player):

- The race a player wants to play;

- The subclass a player wants to play.

And that is really it. Sure, you could buy a player handbook subscription or such, but the basic rules that are free and included in D&D Beyond are sufficient for learning the rules.

For the DM (purchased by DM or person sharing content): 

- If you are running a premade adventure, buy that adventure book (personally, I think premade adventures are too narrow  and would recommend homebrewing a campaign from scratch). Or, if you are homebrewing in a specific setting (say, Ravnica or Ravenloft), you could buy the books for that setting.

- The monster manual - basic rules do not have enough bad guys. 

- (optional) another monster supplement, like Mordenkainen’s Tome of Foes for more monsters.

One other buying versus each buying just their own content:

Advantage to one player buying: You keep a centralised database with all the items you have used; it will reduce their cost on future books if they want to buy more; if you have a player who wants to buy a lot of content anyway, this method is better.

Disadvantages: More expensive for that one player (or the other players could reimburse, but they don’t have the rights to the content after the campaign); one of the players has to have a Master subscription so content can be shared to everyone in the campaign, which has a monthly fee.

Each buying their own content:

Advantages: Logistically easier to ensure everyone pays for what they are going to use; you get to keep your individual content after the campaign; no need for monthly subscription; if you are not sure you want to stick with the game, this method tends to be a little cheaper.

Disadvantages: You do not start building a centralised database for your playgroup; You are unlikely to use the same race/class again, since folks tend to like playing new characters, so owning that race/subclass isn’t actually as helpful as it might seem.

Neither is necessarily better than the other - just pick what works best for your group. 

TL;DR: D&D beyond is great for helping new players navigate the complexity of character creation. It also has nifty tools for actually running the game. Just know that you do not have to spend a lot of money - purchase only what you need and expand your collection if you want (or don’t).

If you want to use stuff that's in a physical book, that's behind a paywall too (and a separate one, as Linklite pointed out: buying physical doesn't give you digital and vice versa, with the exception of the Essentials kit and that's not a one-for-one deal either). It's not really a question of DDB being worth it; it's whether buying into D&D is worth it in the first place, and if so whether it's preferable for you to buy physical or digital. Some people even buy both, if they have the disposable cash and think both have enough value to them to make it worth it.

Of note is that you can try D&D for free, or more likely for very cheap, at first. The Basic Rules have everything you need to play in terms of rules, just not everything you may want, and they're free. You can find them on this website under the Sources (see the pull down menu in the navigation bar at the top of the page) or just follow the link there. The tools on the site, notably the Character Builder, function just fine using only that content, you'll just have limited choices compared to someone who bought sourcebooks here. The reason I say "more likely for very cheap" is that the Basic Rules may not explain how to play clearly enough for you and that they don't include an adventure to play. You can find explanations and help (or watch streamed games to see what it's like, but please keep in mind that experienced players and DMs and a significant production budget will make it look better than what it'll be like for you at first - manage your expectations) and there are free adventures too, but it might be a lot more convenient to buy the Starter Set or Essentials kit. They have an adventure you can play that provides some hand-holding for the beginning DM and they're cheap enough if you share the cost with a group. I'd advise the Essentials kit over the Starter Set because you get a few follow-up adventures for free and a coupon for 50% off the PHB here on DDB, though the Starter Set simplifies everything even more than the kit and for some groups that can be a good thing. In both cases the adventure itself is excellent for new players.

If you decide to stick with it and buy some books, it really comes down to the convenience of a digital ruleset (more portable, cheaper than even Amazon, the toolset to streamline character creation, the possibility of sharing books you own in the toolset with others if you take out a subscription, and being able to cherry pick the content you really want over having to buy complete books) vs the permanency of physical books (you own books while with digital stuff it's really a licence you take out, and you can support local game stores if you are ok with paying more).

Yes!

Quote from ashrimega >>

So my friends and I are looking to start a campaign but none of us have ever actually played before. Dnd Beyond looks super continent and useful but also like it might lock everything behind paywalls. In your opinion is it worth it to buy stuff there?

 
It really all depends on how much time & money you intend to invest into the hobby. The company that makes the game is not the company that runs this website. So if you purchase hardcopy materials they won’t work here, and if you purchase digital materials here you won’t receive any hardcopies with it.

For now I would recommend using it because it consolidates all the free content and makes character creation waaayy simpler. Play the game just using the freebee stuff for a little while and see what you think of both the game and this website’s toolset and make your mind up later. (Even if you decide you love DDB, if you don’t love D&D and don’t plan to play much for whatever reason(s), the website holds little value.)