I can't speak for the PDair version, but I bought a 3 pack on ebay before I got the phone for like 7 bucks. They suprisingly fit quite well. Phone functions exactly the same: all ports are accessible, sliding is not affected, keyboard access is normal.
I also did drop the phone once coming out of the car. The case stayed on and did its job and the phone was not touched.

Having said that, the only problem is that the small tabs that keep each side of the case on are very weak. After first installing the case, it fits tight with no play but after a while it starts to give some play and become loose. And finally, the little tabs that hold the top piece on break off. The third and last one just failed on me. Installing the case once and never taking it off may lengthen the life, but I doubt it will keep them from breaking eventually.

The other problem with these, is that they add a considerable amount of bulk to the phone. Everyone who sees the phone with the case is amazed at how big it is, but when I take the case off they say 'oh that's not bad'. Without the case I don't mind the phone in my pocket, but with the case it almost doesn't fit. For this reason I'm searching for another solution.