Well, I do most of my diving with a couple of high-pressure steel tanks with DIN valves, and most boats have no problem with the DIN attachment. On one boat they thought they didn't have the right adapter, so I put an insert in (my DIN valves are the type that have a screw-in doughnut to change them to yoke). But even there they looked a little harder on the boat and found a DIN adapter.
The main problem is that many boats can't pump higher than 3000 psi. So my steel 100 turns into something more like a 90. I was talking to a shop owner the other day who said he thought that h.p. tanks are better on the beach (better weight characteristics), but he likes l.p. tanks on boats precisely because of the fill pressure issue. Then again, isn't my E7-100 just a rerated l.p. 80?