I use the cp321 although it does not have a belt clip on the reverse.

I keep mine in my jeans pocket.

Clean looking and keeps it safe and sound.

Main complaints about the cp321 are :

Does not have a belt clip/hoop.
Cannot use headfones when n900 is in cp321.
Cant charge it while its in the cp321.

I dont listen to music on mine and I would not even contemplate cooking my n900 by charging it while its encased in a pouch/holster !