A basic flashgrip:
A folding version:
Since they don't add much hassle to bring along, i almost always have this in my bag(or hanging off it) when i go out to shoot with my DSLR.
How do they work?
Flash grips give you a basic extra handle, the more points of contact you have with the camera the better your chance at holding it steady. You'd likely seen many rigs out there, and many of them have two handlegrips. Adding a flashgrip to your camera is like a scaled down version of that. They're mostly styled for DSLRS, but if your video camera has a handle which can rotate to match this, that will work great too.
Ever get hand fatigue in your right hand from holding the camera? That's the camera pulling against your wrist, and adding this second grip will do wonders in solving that.
Do you give up control over buttons/settings?
Possibly, but what i've found is i can retain most of that by positioning the grip close to the body and at a slight angle so i can get at the buttons/rings/etc...