I'd bet extremely heavily against any pretty paint below the waterline for everyday keeping of the boat. If something says it's not meant for underwater applications, I'd believe it.
Even gel is very different when applied onto an exterior surface since it has to be faired to shape--it requires patch additive and is very different from the gloppier stuff that gets sprayed in a mold, where the mold makes the surface/shape right. But even the thick stuff they spray into molds isn't guaranteed to keep water out. A lot of boats will blister if left in the water, even with factory gel.
Some manufacturers not only do gel in the molds, but then barrier coat the gelled bottom prior to bottom anti-fouling paint. Barrier coatings are usually require a BUNCH of coats. They don't have a pretty finish like the paints we're used to for topsides.
Water is terrible for a boat.
"I don't have time to get into it, but he went through a lot." -Pulp Fiction