This is a very good battery grip. It fits perfectly on my Pentax K10D.
You can keep a battery in the battery grip, but you can still have a battery in the camera. This is a disadvantage when you want to charge the battery in the camera, then you must unmount the battery grip to remove the battery.
The battery compartment on the battery grip also provides space for an SD card and a wireless remote control, which is very smart.
I think this is a very good battery grip. Furthermore, it is weather sealed as K10D: n However I am a little disturbed that no AF button is on it, because I only use that button when I use auto focus. However this is probably less important for those using the usual trigger. Otherwise there is the most important buttons with.