My car rental experience lasted over six months, and I ended up with a great deal from AutoSlash. I used the cancel and rebook feature offered by them and the rates for 16 days on Maui went from $680 (cheapest rate I could find) initially to a final rate of $425 from Hertz - this is almost $250 less than the next lowest price I could find.
Every rebooking/cancellation activity was perfect with a fast refund on my cancellations. AutoSlash responded to my email questions quickly, which gave me a sense of confidence in them.
I picked up the car yesterday, and it went perfect.