Thanks Phil;
I guess that is the best answer available on this. I have read those threads you linked to. Although the Subal port and adapter has been available for a while, as I understand it, that same dome in the mirrorless mount is fairly recent. There have been discussions about pros and cons of using the 3.5 vs 4.33 Nauticam ports but I had not seen any where the Zen dome was also compared. I am assuming the 100mm Zen is not simply a glass version of either of the Nauticam ports.
I had actually wanted to avoid getting into the glass vs. acrylic issue, although I probably did not word that well.
Sadly, I have essentially no access to housings and ports where I live and I have to travel to dive, and even my pool access is limited locally, so it is almost impossible for me to handle housings and ports before buying them and hard to test ports and lenses underwater except on dive trips, so I rely heavily on what other people say in making buying decisions.