Couldn't be happier with my Ikelite housing for the 5D mk3. The housing is easy to use and very easy to keep the o-ring grooves clean. Buoyancy of the housing and camera underwater is very close to neutral. The controls give you access to all-but one camera setting.
There are just two negatives that knock it down from 5 stars but not enough to change my recommendation of the housing. First is that you can't access the multi-controller, which means that if you zoom in on an image during image review, you cannot scroll around the image to see if you've got backscatter in the corners of the frame, etc. Second is that the 5510.11 port body that I use with the Ikelite 8" dome is a pain to install and remove. A fellow photgrapher recommended using a rubber strap wrench, which has made the process much easier. That said if you're just shooting a fisheye with the dome, you'll rarely need to remove the port body.
All in all, a fantastic housing for the price. Highly recommended for anyone building an uw rig in this budget range.