This is a hot topic (pun intended) over on the Jayco forums. Seems like Jayco lead the pack with widespread use of tankless water heaters.
Two main manufacturers get the most discussion - Girard and Truma. Girard came with many Jayco's starting around 2016.
People either love the Girard or hate it. No one's in the middle. The latest Girard (Gen III) is less quirkly than the earlier models but it's still something you have to learn to use.
People who love tankless but hate the Girard quirks replace their Girard with a Truma. The Truma's about 3x the cost of a Girard and has to be installed by a licensed Truma dealer.
We have a Gen II Girard in our Jayco and really like it.
Yeah, it took a while to figure out how to make it work well - but we figured it out. That said, if it ever dies, I'll consider replacing it with a Truma.