I have the Canon BG-E6 on my 5DII. It's a well made, good product. I'm happy with it and felt it was a good value. I use grips 95% of the time on all my cameras and have since the 1980s (winders and motor drives back then, and then Power Boosters on Canon film cameras in the early years of the 21st century). I only remove the grip if hiking or cycling with the camera and wanting to temporarily reduce size/weight to a minimum.
Back when I got the 5DII, the new LP-E6 batteries for it were scarce. There were third party batteries around (which I use with older models without a second thought)... BUT, they weren't the new Canon lithium technology, couldn't be charged in the Canon charger. So, check what batteries used by any third party grip you are considering are fully compatible... You might not be able to use any LP-E6 you have in the 3rd party grip, and might not be able to use your Canon charger with their batteries. All this might have changed, if the 3rd party manufacturers have caught up with Canon's battery tech changes.
Third party grips for 20D to 50D and 5D Classic were more easily cloned, since all those cameras used the venerable old BP511/511A batteries.
Oh, and the 7D uses the same LP-E6 batt. packs, and I suspect when it's introduced a 60D will too.