It is an SPL housing. I have a fisheye dome port as well as a flat port. I use a Sigma 10mm Fisheye, Canon 50mm 1.8 II, and most usually Canon 24mm 2.8.
I plan on getting the 1Dx in the water as soon as I have the money for a new housing, probably switch over to Essex Housings. Its risky sure, but if you take care of the housing, clean it, keep the gaskets well lubed, and take your time while assembling it, it is very unlikely that you will have any kind of catastrophic leak.
I've had the 30D in the water for nearly 3 years now with no issues. It has traveled up and down the East Coast and been to Puerto Rico and Nicaragua no problem.