I don't get this item...what is the point?

See if you lost an eye or two and don't have access to an regenerate spell ... this helps out. You could also reskin this for any other body part if you wish

Depends on the rules that your game is using, too. Check out the DMG section about permanent injuries: https://www.dndbeyond.com/sources/dmg/dungeon-masters-workshop#Injuries

Losing an eye gives you disadvantage on sight-based Perception checks as well as ranged attack rolls. An item like this would fix it.

I know it doesn't say so, but eye would be so tempted to let my players use it like Mr Potato Head's eye, able to see through it even when detached.

Confused why this item appears in both xanathar's and Explorer's guide to Wildemount.

Not everyone buys every book. 

Quote from Twitchswitch >>

I know it doesn't say so, but eye would be so tempted to let my players use it like Mr Potato Head's eye, able to see through it even when detached.

 My DM gave me a home-brewed version that works that way.  Currently my most prized magic item; has been useful, hilarious, and often both at the same time!  Completely worth the attunement slot!

Quote from Twitchswitch >>

I know it doesn't say so, but eye would be so tempted to let my players use it like Mr Potato Head's eye, able to see through it even when detached.

 Bad pun, but still funny

What is it worth? In the case that a player wants to sell.

well I just got one enchanted to give me nightvision :)

"....it can’t be removed by anyone other than you, and you can see through the tiny orb as though it were a normal eye." 

My interpretation of this is that you can remove it and place it somewhere to spy on a location or throw it into a room to check it out before you come bursting through the door.  The Point: it's a removable eye that you can still see through even when it's not inside your eye socket.  

There is no mention of distance so maybe you can even mail it via European swallow to a friend across the country and you can literally keep an eye out for them.

Quote from PunkyDrewster81 >>

"....it can’t be removed by anyone other than you, and you can see through the tiny orb as though it were a normal eye." 

My interpretation of this is that you can remove it and place it somewhere to spy on a location or throw it into a room to check it out before you come bursting through the door.  The Point: it's a removable eye that you can still see through even when it's not inside your eye socket.  

There is no mention of distance so maybe you can even mail it via European swallow to a friend across the country and you can literally keep an eye out for them.

 Now that's pun

Quote from Twitchswitch >>

I know it doesn't say so, but eye would be so tempted to let my players use it like Mr Potato Head's eye, able to see through it even when detached.

 Boooo. Bad pun

Talk about having an eye in the back of your head>>>>>  I would put it on my backpack so no one could sneak up behind me. LOL.

As a DM how much should this cost on the black market?

As any common magic item 100 gp 

My 3rd lvl Warlock with patron Genie  (Efreeti)  lost his eye fighting Cryovain but mange to slay that beast with a well-placed eldritch blast when he was trying to flee from the party :D Me and my GM are thinking about a more personalized version of this item made from the tiger eye gemstone because the properties given to this stone in mythology fits really cool with my character. My GM is generous enough to not take away an attunement slot for using such an item. He gave me the option/quest to get my PC his eye back if he manages to find someone with regeneration magic  but I think stuff like that should stay with a character :)

For now his using his fire imp in the form of a flying stone cat with bat wings  (a long story of a very cool ritual my character had to came up with and gather the items needed ) as a crutch. This wound is a really unfortunate result of  a roll for my PC because his tactic for fights  are long range attacks with a juice up EB cantrip and fire spells. 

If this would be a little less common of a magic item, you could have the Detect Magic, or Darkvision spell on at all times tipp make up for the fact that this requires attunement.  Similarly, you could test it like an artificer's prosthetic limb and only have the sink treatment requirement if you have more than one, but that can always be a table rule. 

Seems like a waste of a magic item slot if it doesn't come with any perks. 

Quote from PunkyDrewster81 >>

"....it can’t be removed by anyone other than you, and you can see through the tiny orb as though it were a normal eye." 

My interpretation of this is that you can remove it and place it somewhere to spy on a location or throw it into a room to check it out before you come bursting through the door.  The Point: it's a removable eye that you can still see through even when it's not inside your eye socket.  

There is no mention of distance so maybe you can even mail it via European swallow to a friend across the country and you can literally keep an eye out for them.

Quote from sLabrys >>

While the ersatz eye is embedded in your eye socket, it can’t be removed by anyone other than you, and you can see through the tiny orb as though it were a normal eye.

 

Only when the esatz eye is placed into the eye socket is when it works. Sure you can homebrew it but it sure says that it needs to be on an eye socket to function.

How would all y'all feel about excising the attunement requirement and just making it work in whoever's eyesocket it is in and only come out if the current user takes it out, without the need to spend one attunement?

Somesuch like a Prosthetic Limb essentially.