Tio answer your 20 questions:
1) does if fit securely?
seems too, I've not tightened it up much, and bearing in mind that it's designed for the 122, and the 1150 seems to have more curvature on the screen it seems OK to me.
2) any chance of it damaging the screen (it seems like a mighty small contact area where it clips to the main screen)?
I guess it could damage the screen, but you could fit a rubber patch to prevent the metal contacting the screen. I guess the big problem would be an impact!! but then the screen would probably be knackered anyway.
3) does it leave any marks if you change your mind an take it off?
I haven't tried, but again if you used rubber patch / part of inner tube type fixing it'd probably be OK
4) does it vibrate much?
Does it vibrate - yes but so does the screen, it's not bad, and it'll all depend on what angle you've got it fixed at, and what the terrain is. I haven't noticed it being a distraction, other than the extended height of the screen.
I certainly haven't felt the need to remove it, so I guess it must be an improvement. Lets hope I don't change my mind
Cheers
Dave#...