On a hunch, I types in
www.avisfirst.com and the site is there with a little info. You have to "Activate" your Avis First status on the site.
More free weekends (2 days), up to 8 a year for every three rentals.
They tout special offers, but if the offers at the link are any indication, I don't think anyone is going to be very impressed.
I can't find any information about service levels at all.