I don't have extended warranty experience with Tesla, but we had our Jetta CPO'ed when we bought it. I found out that the selling dealer never filed the paperwork when I took it in for a couple of minor things. Lots of back and forth to make it right. The CPO recently expired, and those minor issues never got fixed, as the service departments couldn't ever figure them out. Based on that experience, I'll just pay more attention to the details of the next used car we buy, and if it comes with a CPO warranty, then so be it. I try to avoid models with high failure rates anyway.