Graham,
You are talking out out of your hat to such a large degree that it's starting to become worrying.
If all you want from a subwoofer is sheer SPLs at ultra low frequencies, then a Submersive, on paper, looks to be a great sub. The thing is, there's a lot more to the different reasons people use subs than that particular quantity alone.
For music lovers disapointed by, for instance a PB13, there are considerations such as upper bass distortion and group delay profiles to be considered, none of which require, or exclude a mahoosive sub from being employed. Once you understand what these qualities are, how they work and what design features of a sub/driver affect them, you may be in a position to make sweeping statements like "sub X is better than sub Y". Because it definitely isn't that simple, I'd keep your powder dry and steer clear of such bold statements.
Certainly stay well clear of suggesting other members actually
buy the sub you prescribe as a pancea based purely on the feedback of users in another country, with significantly different house/room sizes and construction techniques. If it's so clear that the Submersive is your particular silver bullet, then
you take the risk and buy one and then
invite Pollywoggle down to hear
yours.
I'll confess that I didn't know that the Seaton subs offered more than matt black/grittex finishes, but at least two sources I've read from since describe the finishes/veneers as "not bad for a DIY sub" and "okay". Like I say, there are many different reasons to buy a sub and quite a few others as to why you shouldn't or wouldn't. The fact that two entirely different subs cost the same is the least relevant reason going, especially when nobody has heard one of them.
Russell