I'd want this even if I was in like a desolate wasteland type place with little or no water, Look how cool you'd look! Also it seems to have the most coverage of all the cloaks I've seen (based on the art seen on the website) so it'd help with the heat as well, giving you a reason to not take it off when you aren't anywhere near water.

Starting a pirate themed campaign at level 3 I'm playing an artificer and was going to have this as one of my infusions what would i need to make one? 

if you want to make it then it would be a lot less expensive than buying it it says it would take 200 gp 2 workweeks and beating a monster of ac 4-8 for materials so it might be good to be an artificer.

Had a monk who got one of these. He was like an underwater missile, using ki to dash, zooming around and outrunning dolphins and things. He also never took his hood down so the canon was that he basically walked around dressed in a manta ray mascot outfit. Was pretty hilarious.

Bingo. No drowning for the full plate paladin or the heavy weapon master fighter. The joys of magic. *laughs*

the #1 grossest example of poor magic item design.
in 1 uncommon item requiring no attunement and nothing more than the use object interaction you gain a swim speed greater than most aquatic life, the ability to breathe underwater.

compared to ring of swimming which grants a poor swim speed and requires attunement

cap of water breathing which again require attunement as an uncommon.

They need to errata something here. its as bad as the broom of flying vs most other means of gaining flight. maybe if they weren't so focused on pumping out new garbage (spelljammer) instead of refining the existing systems. you know you guys own the rights to the existing material and lore right??? just checking.

at the least the rarity should increase.  

yes. the issue was holding your breath after speaking which then goes straight to con saves. underwater speech is difficult to understand unless the language is designed to be spoke underwater like some of the elementals or tritons so you give disadvantage on perceptions to hear. they DnD team kind of left basic questions unanswered like if i can see 2 miles how far can i hear normally? and id say since spell effects allow for things to be heard loudly within 300 feet than you can hear Normal things in the same radius and outside that is disadvantage while inside 30 feet is advantage for normal speech. add whispering to impose another stacking -5 disadvantage. with dnd next i encourage more check vs dc (8+prof+stat) this way you can apply stacking adv and disadv to skill checks.

another good model is
8+(profx2) [+/-] 5 dm determined circumstances [+/-] 5 adv/disadv
this creates a minimum range of 0 for just auto success and a maximum range of 30 for difficult yet achievable dc's by players at the given proficiency range.

I would rule that with the Cap you could also wear a magical Cloak of some kind. (Obviously not the Cloak of the Manta Ray)

when an action is used to pull the hood up, it traps a bubble of air within its folds; thus allowing you to breathe while underwater.  I suppose the GM could also it to work against poisonous gases, or at least provide a small degree of protection from.

As an artificer, How many cloaks can I make? Can I make 4 in one go or do I make one cloak at a time, during short or long rest?

My bard bought one so he could give head in a hot tub.

I think you are forgetting that the player isn't the only one who can pull it up or down

Quote from Nagog >>

So does the existence of this item make the Cap of Water Breathing obsolete, particularly for Artificers who can create both? For a while I assumed this needed Attunement, but it doesn't so... Why bother with a Cap of Water Breathing?

 Late reply, but the answer is item type. Normally you can only equip 1 item of each type (armor, books, cloaks, ect) so this being a cloak completes with some other items available.