I signed up for the full coverage with Amex.
As I read the fine print, it seems to cover just about everything, including the noxious "loss of service" charges they like to throw in there.
The best part is, it's only $24.95 per rental, up to 40 days (IIRC), so a rental of a week or two averages out to bupkus per day, and the peace of mind seemed worth it to me.