We've developed our own special formula suction jelly, that sticks to your phone easily without leaving lasting marks.
As long as the screen protector is at least 68mm wide it should fit fine.
Absolutely not, we've developed our suction gel so that whilst giving a strong bond to your screen, any marks left behind are as easy to wipe away easily after use.
VR Cups are designed to maximise field of view while fitting most handsets, even those with buttons in awkward places.
As long as your mobile works with apps built for Google Cardboard and has a screen size at least 68mm wide, they should be fine.