There are some issues that make it difficult to look good.
Main one is if a weapon has an offset or the player is sprinting it will move the mesh that attaches to the 1st person camera to give that effect. Not a big deal for a uniform glass texture but it means you can't get the inside of helmet itself to obscure parts of the screen.
The other issue it may or may not work properly on ultrawide displays which I know is a very small minority of users but it is something that should be kept in mind.










