What have been your experience with allowing an extra feat at character creation?  This would not be for level 1s but likely 3 or 4.  Always considered it but had never actually done it.  But after following the dnd playtest (and its unique first level feats) I think it might add a nice diversity to the group. 

Even considering someone's variant of starting with non heroic starting stats and allowing both a stat bump and Feat at the 4th level points.

My players loved it. They loved that their characters had this sort of "signature move" right off the bat that distinguished them even within their class. One player took the Observant feat, and it completely changed how a lot of the scenarios played out.

The downside was that I was using a pre-written adventure (Lost Mines of Phandelver), and the players essentially started, functionally, with an additional level (minus the HP boost). So they absolutely steamrolled the adventure which, to be fair, is designed to be pretty beginner friendly and not particularly challenge the players. So I'm fully in support of a free feat at level one, just remember that you need to keep in mind that additional power level when balancing encounters.

I think with the current campaign I have planned i have been worried it is tuned a little too high(at least what I have in my head atm) so that might be just fine.  

I give a background and a bonus feat and my players do get pretty excited about it. I've had to add extra feats to my monsters, and it has worked out pretty well.

I think it's fine, especially when the game has given feats as part (or in lieu) of a background feature since Spelljammer: Adventures in Space, I believe. As TransmorpherDDS rightly points out, it's a "signature move", an extra tool in that character's kit that nobody else has and offers them an opportunity to help the party in an unexpected way. If you're worried about it being overpowered, give feats and other abilities to enemies (one of my favourites was a Goblin with the Chef feat; Yezjhev would command his warband to eat to heal themselves, and they would respond with "yes, chef!"). Don't nerf the players; buff the monsters and give them something that stands out.

Thank you, I truly appreciate it.

Not at character creation, but as a result of solid roleplay, or as a downtime/training opportunity I have given the party choice of some new feats...often either homebrewed or feats they ordinarily might not get access to. 

My advice though is that if you're going to give them choice of an extra feat at character creation, you will need to limit the options if you've got any power gamers/min-maxers in the party. Otherwise, granting new feats can be really fun for players.

One thing I've wanted to test out is allowing the players a free feat at level one, but limiting them to the half-feats,  minus the Ability Score Increase that half-feats come with. It would prevent players from taking the really gamebreaking feats like Sharpshooter or Polearm Master. There's still some really potent feats in that categroy... the Shadow/Fey Touched feats are already more potent than some of the fully dedicated feats (I think they're superior to Magic Initiate for most builds, for example), but it could be a way to give players a free feat that will, on average, be easier to balance around.

I have been running a game where the players chose standard array or point buy at creation, then get to add points AND a feat at every ASI. The players love the heck out of it. It is definitely overlocking the party, but I have not found it too big a deal to adjust.

I had one DM allow me to use the Blade Master (UA) feat while playing a Shifter Samuria Fighter. The amount of flavor and usefulness of that mechanic was really cool

I’ve come to support having a single bonus / background feat at level one (not including the human bonus).  Simultaneously I also take a hard look at feats to make sure the players aren’t getting something overpowered at 1st level.  There are things that I like about UA but there are plenty of things I don’t.

I like the idea of giving the characters a little more identity with the extra feat.

Quote from HeroZero >>

I like the idea of giving the characters a little more identity with the extra feat.

 I do it, and it does let the players tune their characters a bit more.  I do exclude any feat that gives a 2nd level spell, though, as those unbalance things too much.

Those would be the fey, and shadow touched ones?  Are there any others?

Quote from HeroZero >>

Those would be the fey, and shadow touched ones?  Are there any others?

 The elven racial feats (Fey Teleportation, Wood Elf Magic, Drow Magic) all give a 2nd level as well.

I may not end up restricting them for the current game in mind. But if/when I do a level 1 start I think I would tend to agree with that limitation.

Have you figured out how to do this via D&D Beyond or only via P&P (Pen & Paper) for you younger folks.  I'm trying to get my players to build via D&D Beyond but I can't figure out how to get them an extra feat at 1st level (as long as they meet prerequisites).

Quote from Zaymot >>

Have you figured out how to do this via D&D Beyond or only via P&P (Pen & Paper) for you younger folks.  I'm trying to get my players to build via D&D Beyond but I can't figure out how to get them an extra feat at 1st level (as long as they meet prerequisites).

 It's fairly easy but you need to do it on a finished character sheet rather than at creation. Once the character is done they need to go to the Features and Traits section of the character sheet and scroll to the bottom where theyt'll see a click box for Manage Feats. Click that and it'll give them the list of feats and they can just select the one they want