I came across the Pixel battery grip for the 5DMIII (there is a new version now). I'd like to know if anyone has some experience with it, and could share his/her thoughts, since it is three times cheaper than Canon's.
From the photos, the battery tray itself does not appear to be as well built and it appears to involve less metal in the construction. The build quality on the Canon grip is outstandingly solid. It doesn't appear that the construction is all that bad on this one, but there definitely appear to be some quality differences in the battery tray itself.
That said, it's clearly a very close clone of the Canon grip. They basically just moved the power switch and shrunk the wheel for attaching it. It wouldn't surprise me if it is worth the money, but I also still think the Canon grip is worth the money. I personally own the Canon grip. I have no direct experience with the third party one. I'm just working from what I can see in the photos.