This helm right here, my dear friends, is single peace of "Helm of DM headache".

Give to players if you feel brave and confident about your world-building skills.

Honestly looking for a way to give my artificer permanent, or at least easy access to a workshop. The heals seems to be the best way too go rn

I would advise customizing this or any other "teleportation item" so that it:

• Teleports to a singular pre-established location  or
• Requires a known circle to teleport to

Or does not allow it to be recharged. i think the recharging is what makes it extremely powerful.

https://www.dndbeyond.com/magic-items/rod-of-security

I am thinking of giving it 1 charge and 1d4 days before you can use it again.

Why is this a "rare" item. IMO it should be "very rare" at the least, as it casts a 7th level spell and regains charges.

Remember that teleport is a level 7 spell, meaning free teleportation is an ability suitable for level 13 players. So I don't recommend giving the item to level 10 players or lower, this is a level 11-15 category item. I recommend making this item a "very rare" item, and potentially making it available to party's who can't naturally get the teleportation spell.
As for lower level party's, I recommend tweaking the item to only teleport to teleportation circles that the wearer has memorised, functioning as a teleportation circle spell. This way, the party can use it to return to major areas they have visited and helped, but can't attempt to infiltrate hostile areas or go to completely new areas. This works as a rare item for partys of level 6-10.

I agree with the other comments that a rechargeable item that casts a 7th level spell multiple times a day should be more rare than "rare." That said, I wouldn't nerf it any more than that. If you're afraid of PCs circumventing your adventures, remember Teleporting is risky, 7th Level Wizards get Mordenkainen's Private Sanctum, 11th Level Clerics get Forbiddance, and both of those spells can be made permanent. It's entirely plausible and within the rules that your Big Bad Evil Guys have taken the time to harden their fortresses against Teleport shenanigans.

I'm going to teleport to the moon

I've seen a lot of "don't let your players have this" However I offer counter argument. It can actually open up a larger play area and give you variation in local.

Party got to level 10, they spent a while stockpiling coin and a few lower tier magic items, while working in and around the city of Waterdeep and managed to make a trade with a Magic Item Collector to get this helm, on the condition that they assist him. If they ever come across a circle of teleportation they call him using sending, he would then cast scrying and they let him study the circle using the scrying. As part of this agreement there is an investment plan. He's wiling to pay a tidy sum of coin in exchange for their efforts.

They pooled their money and spent close to 30,000 on it, that represented the majority of the reward money from like, 2-3 major quests and 3-4 minor quests. I mean I'll be honest they also spent 2 weeks of downtime trying to see if there was any way to get across the map faster. They managed to roll high so they learned about Wind Walk, Word of Recall and Teleport. 2 of those they will actually be able to cast soon anyways

I was thinking of getting my dm on board with being able to land on creatures, causing damage, then teleporting above enemies with my barbarian and crushing them. lol

So im a rouge and I want to turn this into a dagger, is that possible? 

I made a ring version of this, but with the 'self only' stipulation - limiting use for party hopping, but allowing for the wearer to teleport somewhere and back to the party in situations where it is warranted - I think that solves some of the concern with having teleportation being too available.  

Is it possible to counterspell this type of teleportation?

Our BBEG has one and just escaped our last fight with 12hp remaining by using an item to cast Teleport. 😭

Yes.

"Rare." 

No. This is a Legendary or Artifact. 

I was thinking about giving my players a Folding boat, or a dagger of venom, or even a ring of feather falling. But then I thought Nah those rare magic items are too overpowered.
Now a helm of teleportation. That's where it's at.