Our last and first coach was bought used from a camping world mega sale. As a newbie to the rv lifestyle i bought their warranty with 5 years of coverage. That cost $10,000........ouch.
I did use it on 3 or 4 occasions and never had a problem with them covering the costs.
That said I would suggest not to buy one but take that money and put it in the bank and use that for future expected repairs. If i had done that my bank account would be 8,000 larger.
The adds i see in magazines showing the cost for a refigerator, hot water heater etc are showing the replacement cost. They seldom will replace but fix the offending part. That is my experience others will be different.