I don't know if they've changed since, but in the last 4WDAction fridge comparison the Primus scored very poorly (if I remember correctly). The comments at the time were along the lines of "looked good, spec sheet looked good, but due to poor/thin insulation and sub-optimal programming, used a lot of battery power and didn't hold temperature well".
I'll see if I can dig back through the archives and find out what issue the fridge comparo was in.
If you're buying on price, I'd be checking out a factory-seconds waeco (
www.getawaeco.com.au) before looking at a Primus. Keep an eye out, I've seen 40L ones as cheap as $750 from time to time. Also, with the new models of Waeco released recently, you might find a shop wanting to do run-out specials on any remaining old-model stock too.
Good luck!
Matto