I don't think it's correct that they only work with Sixt. I've gotten several notices in the last week or so about rebookings with Thrifty. Unfortunately, these are bookings that I made months ago and for which I long ago found cheaper alternatives.
Autoslash doesn't have any value to me if I can't count on it working. If i have to manually recheck the prices myself I'll just rebook them myself.
If Thrifty's back on the table, then I assume Dollar is too?
I'm not a *huge* fan of Dollar/Thrifty, but at certain locations I'd have no problem with them.
Contrasted to the Payless type stuff of the world, which I avoid at almost all costs. (I say "almost" because I did rent from Advantage recently thanks to some wacky pricing going on during Spring Break at PHX.)