For me its kinda bulky.Before the 5DII I used Pentax K10 and K20D cameras.The grips for those were more compact, more solidly attached with no flex whatsoever, and you didn't have to remove the battery or battery door off the camera to attach the grip.I wish Canon would have adopted a similar approach with its mid range dslr's.
If I had it to do over I probably would not order the grip for my 5DII.When griped with a big lens on my tripod, the rig is as bulky, and actually heavier than my 4x5 field camera , and with inferior image quality for the kind of stuff I like to shoot (still life and landscape) This has had me contemplating just getting rid of the whole enchilada and just sticking with my 4x5, and T2i for snaps, however without the grip, on my Nodal Ninja 5 pano head, the possibilities for some very high resolution mosaics, in a somewhat compact package, without the cost of sheet film has kept me from abandoning my 5DII.
It seems to me if you have really big hands, and shoot mostly hand held, the 5DII grip might be advantageous.I know with my T2i its battery grip makes the whole camera feel better ->for me<-, but on my 5DII its grip makes the camera feel too bulky ->for me<-, and too flexy when its tripod mounted with big lenses.The genuine Canon grips themselves are of pretty decent quality in materials and build, no complaints there.Probably best to see if you can find a local dealer to mount up a grip for you so you can test drive it yourself 
C