Another thing, my cell has side buttons, if the holder grips on the sides of the cell, its going to depress the buttons constantly. not so great. EDIT: I see the holder can be swivelled, so could hold the phone on the top/bottom. problem solved.
My holder is quite steady while driving and wobble is minimum. Should last you for quite a while depends how you use your holder, general build quality should be ok for most of the holder, but please take it off your windscreen when you don't use it, keep on exposing the silicon suction cup under direct sunlight and high temp will just speed up the wearing of it and eventually will no longer be able to hold it to the glass.
I use my holder when I use the GPS navigation in my car only. Can hold the phone both vertically and horizontally without any problems and/or blocking the keys/speakers.