I have not used one, I have seen it used on a friend's device. They get very very good reviews for the intended purpose to keep safe the device it encloses.
Can't live without it! Awesome protection for my BB ( I work in a harsh environment). You won't be disappointed with it. You might have some problems with the 1st layer of protection(membrane to cover screen and keys). I will post back later an easy fix for putting it on with the least amount of air bubbles.
I have one for each pearl,curve and my 8820 best thing arund. I dropped mine from a upper deck about 12 feet onto concrete and it worked fine. Sometime the SIM card needs to be removed and put back in after a hard jolt like that. Better than the alternative.