I bought mine well used from original owners who had all service records and a Good Sam ext warranty. Found out that it was still covered after all these years and I could extended year by year.
I have been doing some repairs getting it to my standards of road worthy and the ext warranty picks up whatever parts are covered. In my case I think it is a benefit. If I was the original owners when it was new and didn't want to worry about the expensive diesel engine or trans repair soon after new MH expired I would do it for peace of mind. Of course I could also put aside some money each year and say after 19 years I would have had x amount of dollars that I could cover that but if the engine failed right outside of new MH warranty I would not have saved that much to cover it. The side benefit is that it covers a lot (not all) of the systems from refrigerator to ice maker that can wear out or break after years of full time use.