Maybe DNV is "Det Norske Veritas", which seems to be the name of an organization related to marine insurance.
As near as I can figure out, if most of the pumps that allow a submarine to surface fail, the submarine may be unable to surface. And the passengers die. Again, if an underwater window breaks, all or part of the ship could flood, and drawn passengers. Could that affect insurance rates? Or am I guessing wrong?
Of course, you could back up the pumps with compressed air and ballast that you can release. But still, I think submarines have greater risks. Even an underwater window that breaks could cause serious flooding.
Nonetheless, I think a recreational submarine sounds like a very cool idea. Especially if it were a lot cheaper.
Of course, it would be more interesting for sight seeing in clear water than muddy water.
One obvious application for submerged vessels, that might justify their price, is smuggling. Do these boats look practical for that?
Smuggling or not, if you a submerged vessel is detected, before or after surfacing, maybe the local version of the Coast Guard would blow you up, on the assumption your were up to no good.
Also, I think a slightly submerged vessel could be a hidden hazard to navigation.
