Does anyone have an opinion or experience with third party battery grips for the Canon 7D? I see them advertised on eBay for all kinds of prices from third-party grips, some with remote controls and readouts. The main reason I am interested in these grips is that I was at the point defiance zoo with my 7D and the 70 to 300 camera on lands added to it, my right hand got pretty tired at the end of the day. I was thinking maybe with the grip added that have more support for my hand while shooting.