These are really useful, I lost one and replaced it because I missed the convenience of it straight away. They're extremely well made, good positive clip that's never come close to coming detached, solid plastic and a nice positive knurling on the case which makes it easier to grip if your hands are wet.
The case itself is very slim, I tend to wear it on the hip and it sits very close to your body so that you can barely notice the phone. This stops it getting caught on car doors, people on the train etc which I've found to be a problem with other designs that 'stand off' from the body or are more bulky. It also means it disappears under clothing so you don't look like 'that guy' with a phone in a pouch on his belt! That's what I tell my self anyway.
The clip is so secure it's replaced my arm band when I go running - you can easily pull the phone out to check and it slips back in very positively. The stand on the back of the case is also a great feature, completely flush so it doesn't snag, a little fiddly to get out but that's mostly because it's solidly made which is exactly what you want.