But good gimbals are pretty expensive. Last time I checked the wimberley was almost GBP 500+, ouch!.
I've been looking at the manfrotto 393 heavy lens support today, it's substantially cheaper while not having the ergonomics. It appears to function pretty much like a gimbal but funnily manfrotto advertises it as being for heavier lenses on a 'monopod' ... How would you rate it?
I have the Manfrotto 393 (aka "Poor Man's Gimbal Head" )

, and I use it with a gripped 7D and the 100-400 on a tripod. It is a very stable support for the camera/lens, and I feel it is definitely helping me get better shots.
A few weeks ago, I was shooting a Rough-legged Hawk hunting, and having the steady support really helped. Rough legs hunt by flying over a field, and then hovering in mid-air, when it sees a likely target, and then diving on it. Handheld, I'd have been able to get a few shots, but the bird would end up all over the frame in successive images. With the 393, I could keep the bird rock steady in the center, right with the focus point.
It's a similar story for me with Harriers. They swoop along low over a field (10-15 feet, maybe 20), and the 393 helps me keep everything steady.
The only issues I have with it are that the pan motion friction is not nearly as easy to adjust as on other gimbals, and when shooting birds high and close, the second "side" gets in the way of your shooting hand.
But for less than 1/3 the price of a Wimberly, for me, for now, it is perfectly fine.