It's a nice little strobe afor topside work, but even there it was dwarfed by its big brother the FL-40, which if I am not mistaken was just discontinued and was very expensive.
I think the real difficulty with the housed FL-20 is that it will necessarily be closely attached to the camera housing rather than on an arm so that you can get it away from the housing, thereby reducing backscatter. Hope this makes sense, it's early and I haven't had my Turkey yet.
Don't forget there's also the housing for the Olympus WAL that fits on to the camera housing. That's a first for Oly too I think.
Good luck, we'll be watching for your photos!
TedJ