I don't have an extended warranty, don't believe it is a cost advantage and wouldn't recommend one. That said, there are people who feel differently, people who can't or don't want to perform maintenance on their RV for a variety of reasons. For them, an extended warranty may be viewed as an advantage worth the cost. I don't know what category you place yourself in, so any recommendation would be a "best guess"....
There's a lot to think about and a lot of research that should be done before dropping $1500-3500 or even more on a "if it breaks" type of policy.
I have no investment in any company that sells "extended warranties" and have no previous experience with this company, but this website has some good information on what to expect and more importantly, what "NOT" to expect:
http://www.rv-dreams.com/rv-extended-warranties.html