Thrifty rates beat Avis hands-down... Should I risk it? (SAN-PHX, one way in an SUV)

Looking for 9-days SUV hire between San Diego and Phoenix in August, with unlimited mileage.

The best rates with Avis, using my Avis Preferred membership and BA discount AWD number is £459.47 for a Ford Escape, or £483.28 for a Ford Edge.

Thrify is offering £299 for a Jeep Grand Cherokee.

I have never hired with Thrifty before.... Aside from missing out on my fast checkout with my Avis Preferred card and my BA loyalty points, what other differences would I notice?

* Are the cars still less than 12 months old?
* Are the cars clean?
* Will Thrifty still have a big selection of cars at SAN (i.e. if I hated the vehicle they'd given me (unlikely I know, but it has happened before!), would I have some wriggle room for another model in same category)?

How come Thrifty can be so much cheaper than the likes of Avis / Hertz? Where's the catch?

Thanks for your help / advice. Always a big decision to move away from a brand you trust, but welcome your comments...

Thrifty is fine. You can sign up for their blue chip program to make pick up quick.

One thing, be sure to check price closely. Avis give you total price right away. Thrifty hides the one way charge, and on the last page springs it on you.