I have the E1 on my 7d... I dont have a grip on my 7d... I bought one of those cheapie ebay ones that comes with the mounting plate on the bottom of the camera and removed the ebay strap, added the E1... took some finesse because the plates want the nylon straps to bend in almost a 90 degree angle and when new... good luck. Anyways I got it to work and has served me well... I dont like the rubber inside feel of the ebay grips... and even the E2 that neuro posted, while nice, appears to be more narrow than the E1, and isn't quite the same...
Got my ebay grip.... works as advertized, however I wish I could feel more secure, it seems like something will give and my 5d will crash to the ground with the 70-200ii attached
Is it secured with a plastic piece? I love the arca-swiss plates that I have on both, they even have threading for a strap/other tripod mount but are secured so tight it feels like part of the camera.