I have had a CS extended warranty on my 09 SG for several years. I have used it at the dealer four times with no problems. They seem to pay quick and have not protested any claims. I would recommend them.
I don't know about the warranty, but I wouldn't hesitate to buy a rental bike. Any damage they may have suffered is usually only cosmetic & repaired before the next rental and they're generally well maintained - regular fluid changes, etc.
I bought a bike from eaglerider. It had 40k on it, was in good shape and had regular maintenance. I've had it almost a year and 5000 miles with no problems. After I left their dealer with the bike, I realized the left speaker wasn't working and that night found that the ignition switch wouldn't lock. I contacted the salesman when I got home and, since I live 1200 miles away, he told me to take it to a local Harley dealer and send him an estimate for getting both changed and they would pay it. I told him I prefer to do it myself and he ordered ordered the speaker and ignition switch and sent them to me. I haven't had any other problems with the bike. I wouldn't hesitate to buy another one from them.