I have the 100mm non IS version and i really like it, great for super macro stuff. I added a 'woody' dipotre which is a wet mount lens which will make ur super macro shots even closer.
I havent found any issues with the exposure that 'Slashmagurk' notices due to camera shake. I have a pair of inon 240s and can comfortable shoot on 1/200th and f16,22,29 for macro shots. And yeah u will throw our shots, but this is the world of macro shooting, the DoF is small and getting the eyes or focal point in sharp focus is hard, but worth the effort!
I have the 10-17 tokina too, bought specifically for u/w use and stuck it behind the nauticam 8.5" dome and its amazing at how easy to use it is to get nice clear WA shots.
I also use my kit lens, the 18-55 for some 'standard' shots, like fish portraits, oversized macro stuff like frogfish and some full body shots of fish like sweetlips, where the 10-17 makes them look miles away!
I will in time add a Kenko 1.4x and the smaller 4" dome for CFWA work but money is an issue at the moment. Trying CFWA the other day with my large dome didnt work, i just managed to put a small scratch in the front of the dome as the 10-17 can focus so close that when looking through the viewfinder its sometime hard to guage how close you really are!
The zen vs the nauticam is price vs acryllic or glass question for me.
Accessory-wise, i added the lanyard grab handle, perfect for the boat boys to hand it down to you! A small Fix focus light for night dive work, Stix bouyancy arms are useful too to keep the weight out of the system. I didnt add the larger viewfinder to my kit for a price reason, and find it fine without, but having never looked through one with a larger veiwfinder i cant comment. Some people say once u look through one, u wont want to dive without one, so my bank balance told me "dont look through!"
Olly