The underwriter for the policy is probably too small for AM Best, or not a general insurer. Most states consider these policies to be insurance and are regulated by the state insurance commission, but the insurance industry does not consider them that way.
The underwriter on my RV Shield policy is Butler Financial Solutions of Alabama. I suspect they may re-insure as well, so there may be multiple layers. I've had the policy since November 2006 and have made a dozen claims, all handled promptly. If the repair shop does not accept credit card payment over the phone, I pay with my own credit card or check and I get a check from the company in 2-3 weeks. My own favorite shop stopped accepting direct payment from any policy other than they one they sell, but they still file claim for me and I get reimbursed. Check with your dealer to see if it is the same. Usually the service dept wants to get the repair business anyway, even though the sales dept wants to sell their own service policy. They make big bucks selling these policies.
I'd like to say that all extended warranties are reliable, but there have been a few failures.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL