Changing ISO underwater becomes important when shooting video. For photos you will generally keep the camera on base ISO so its really less of an issue for stills.
Also, to chime in on optical vs. electronic strobe trigger, for what its worth, the only downside I see to the electronic trigger on the Ike bulkhead, besides for not being able to handle TTL with a non-Ike strobe, is that the electronic sync cord is a little more expensive. But the reality is that many great u/w photographers use manual strobe control anyway so the TTL issue becomes moot.
I shoot S&S YS strobes with an Ike housing and Ike to S&S sync cord and get reliable results.