I had the $5 ones on my HTC Tornado, and they actually held the phone in pretty well. The problem was that the T-mobile version of the Tornado had that ugly antannae hump which the case would use as a hitch point. End result is taking it in/out put a minor amount of wear on the paint in that location.
Not enough to be concerned about, otherwise it was a decent case.
The real problem is that it IS cheap plastic... I dropped my Tornado once, and it survived the fall, but the holster snapped in two.
So I spend another $5...
