We use the Forespar Marlon fittings. I had a bronze valve fail in my hands - in dry dock
as I was doing "maintenance" on it. It was a gate valve, a bad design, though from a top quality manufacturer from the 70s, so it lasted 40 years. As we gradually work
on the boat, we are replacing the old bronze ones with Marlon. It's a tough choice though, bronze is appealing in many ways, but what convinced me is the corrosion
issue. Especially if the through hulls are bonded together, then you provide a current
path for electrolytic corrosion if you stay in a "hot" marina.
Marlon needs regular lubrication (mineral oil
, etc) and regular operation, at least every few months they should be opened/closed. And they need to be installed correctly with a mounting plate, bolts, etc. It's non-trivial.