Hi Jim and Mark, I so much appreciate your generosity, time, experience and opinions. I think the Zen 170 mm dome is pretty new, I also didn't find out much about it on their site - it was recommmended as a possibly good fit considering all the things you mentioned above - cost, but even more than that, the drag while kicking against currents, distant sites, etc., and also, the travel problems associated with a DSLR, housing, camera, 2 lenses, 2 ports, 2 strobes and all the accompanying arms, cords, light, batteries, chargers, plus dive gear. It is a glass port, so that's nice, and it will be mated with a 40 mm extension ring - the research that Reef Photo did indicated the corners would be sharp but might need a diopter for CFWA - I'm going to give it a try. The trouble with my Sea & Sea port is that it required both an adaptor and an extension, so the two rings were problematic for me to get apart (I'm not Mr. Atlas!).
I'd love to still be able to do over/unders, but if that's the price for this "mini-dome", OK, I'll live with it. I'm diving the SoCal oil rigs this weekend with the combo, so I'll let you know what I think!
I used the Nauticam with macro this weekend shore diving at Catalina Island and really really liked both the housing and the 60mm port - crisp, sharp shots, some at minimum focusing distance, the "eye" of a giant kelpfish in perfect focus, e.g.
Hats off to you!