Parents' house has a Regency unit since early 2000s. Very cozy radiant heat and will heat whole house on fairly cold days with the blower going. Milivolt system so will work even during power outage, which we made use of many times. It runs a lot during the colder months, sometimes at much as 10 hours a day. Has needed a few milivolt generators, two gas valves, and last year a new blower. Gas valves went out due to dirty gas and old cruddy pipes here, and the fact milivolt valves are weaker and more vulnerable to fouling. Milivolt generators simply wear out with time, and that fan motor had a lot of hours on it when one of the bearings started squealing. Spread over that many years, a small price for the comfort it brings.
At the price point most residential stuff is built to, there probably aren't any brands out there that are tanks that will just go decades without needing any parts or service.