I bought a Warrentech 6yr/100k on the 99 SL600 that I bought used in January. The plan included electrical systems as well as the normal stuff. Before I bought it, I checked with the independent shop that does my work and they told me that they have no problems collecting claims from that company.
I have had one issue in the ADS system that required a sensor replacement and it was paid with no question. They paid the dealer direct so I didn't have to be involved in the billing process.
So far, so good.