Sits firmly on the phone and on the arm

Very precisely, perhaps precisely because needs to get to the phone in the envelope approach somewhat coarser one already.
With my three-layer winter gear, it is also not so easy to close the Velcro fastener. The tab for that is a bit too short for my taste. So if you have very strong upper arms must be set to something fumbling.

Processing I find really great and the touch screen is easy to operate even by a thin jogging gloves.
Another little tip for people allow tracking their running route via GPS: Only let the Galaxy wait for a stationary GPS signal, then it clamps into the casing. This is slightly faster than the Samsung GPS has received through the shell. Great dropouts I can not find the GPS.