One more thing to think about… If something happens, who decides what type of fix they will use, and who chooses the plumber/repair company?
It’s possible that a warranty company might be affiliated in some way with a plumbing company, and they could come out and give you a $10,000 bill for a $6,000 service, and/or cover only an inferior type of repair, too. Hopefully, this would be illegal (I don’t know), but it could still happen, and you would have to spend a lot of time and money trying to make things right (and probably not succeeding).
That’s why it’s important to check all the fine print and look at exclusions and restrictions.