Could be very similar, and the jist I get is that the HM-1 isn't any groundbreaking science. You're probably in the ballpark there.
I do like the smaller diaphragm size, though- it is said by the old-guard gurus of the sound trade that a smaller diaphragm will give up a more accurate image. I'm going to have a first shot at finding out for myself.
A larger bass cab will give you more bottom than a smaller cab, no matter what the maker of the smaller cab says in their advertising. Volume of air moving can't really be gotten around- some things just come down to simple physics.
So on this premise, I'm pretty interested in getting the results. And yeah, if I hate it, I'm sending it back!