It doesn't cost much but this windscreen mount is, nevertheless, a complete waste of money. In winter, when windows attract condensation, the suction pad pops off due to the high moisture content.
Then, if you heat your window to remove that condensation, well, you can guarantee the sucker will detach itself within minutes because it has dried-out.
My £150 tom-tom satellite navigator repeatedly fell off when I was driving - dangerous if I was referring to it on a busy road, because of the sudden distraction - and in fact now has a scratched screen due to catapulting onto the floor when the suction pad of this window mount popped off for the umpteenth time.
I drive a company car, and didn't want a Tom-tom mount that glued to the dashboard (obviously because it's not my car), but because this useless device didn't do its job, I'm now left with the Tom-tom resting on the passenger seat, where I can't see it unless I take my eyes off the road and risk a collision..