The Belt Clip works really well and though it felt a bit flimsy off the unit, once attached it clips securely to the straps on my rucksack allowing the unit to unclip with ease. The actual clip element remains attached to your bag, belt etc which means you don't have to re-clip it every time. There's a small circular button that screws to the back of the GPS unit and this, in turn, is what holds the unit to the clip. Simples!
The only downside is that Garmin still don't supply a back that is compatible with the HCX models, or any of the Etrex range with the SD card slot. This means that the back which is supplied with the belt clip is useless and you have to use the one supplied with your original Garmin Unit. This is fine if you only ever use the belt clip, but I have a handlebar clip too and this needs to be taken off each time I use the belt clip. Picky perhaps, but if Garmin supplied the correct back then the process would be much easier. It would also mean I don't have a drawer full of non compatible Etrex backs!
As I said, good, but not great.