Is there a clear advantage of the SEA & SEA housings? Why are they so expensive compared to the Ikelite ones?
Haring, I think the real question here is why are Ikelite housings so cheap compared to every other brand? They are made of acrylic (as opposed to aluminum), and may not have all the features of a more expensive housing. Don't get me wrong; Ikelite isn't bad (I've have a couple different Ike housings), but they're also not as good nor as high-quality as others.
For the last several years I've had an Aquatica housing which I absolutely love. The body/port connection is much more secure than Ikelite's, and the controls fit me quite well. I can also do a lot more with it than I could with an Ikelite.