Some of these are just different implementations of the same idea... some of these are for different purposes.
The "steadi-cam" is basically a gimbaled mount platform that you hand-hold (although they do make a vest that you can wear... the vest has an arm that attaches to the mount so that you don't get fatigue. Hand-holding is great for short-duration clips... but you wouldn't necessarily want to be doing that for an extended shot ... much less all day long.
The idea is to throw some weight below the camera to keep the camera upright... but there's a problem with this. You can't just throw *any* amount of weight down there. If the weight isn't enough it wont hold the camera upright. But If the weight is too much then when you move the camera sideways, "inertia" will cause the heaviest mass to want to stand still. This will cause the camera to tilt. The idea is to tune the mount so that it's *just* enough to hold the camera upright but not much more.
It still takes practice to learn to use one of these stabilizing gimbal mounts. I personally don't shoot video, but have friends who do. I've used the Merlin Steadicam and it's definitely a skill that you learn.
The X-grip is intended for getting shots from a low angle.
When you hold a mount at arms length, your arm is going to tend to absorb some of the jarring motion that would otherwise be caused by you walking around. A shoulder mount will have an advantage for shots where you aren't chasing the action (by walking or running) but isn't going to do much to absorb jarring if you do have to start chasing the action.
Tim Campbell
5D III, 5D IV, 60Da
