Mounting LCD Viewfinder

[Doc J]

Has anyone used an LCD viewfinder that you had to actually mount on the camera? I know some just attach with bands, but the good ones look like you actually have to mount a glass plate with adhesive to the LCD. Most people say they don't seem to mind as its just extra protection, but it makes me nervous. Here's the one I'm looking at.

GGS LCD Viewfinder Loupes 3X For 7D 5DII 550D 600D ab41 | eBay

Any opinions on this? Preferably from someone who either has done it or seen it in person.