I've used an Energy Star Magic Chef 3.5 cf dorm fridge for 5 years now, and it's worked very well. I did add extra rigid insulation on the back, top, and bottom (not sides, as that's where it throws off its heat. I have 2x6 Volt FLAs and a 2000 W inverter. In the morning, my battery SOC is usually still over 90%, sometimes mid 80s. I have a solar panel, so it charges up quickly once the sun comes out.
I did run a few tests with a Kill-a-Watt meter in mild early summer weather (around 75 degrees daytime) I measured three multi-day stretches with daily consumption of 350, 335, and 278 watt hours. These are very low numbers, corresponding to about a 110 kWh/year, or half its Energy Star label rated consumption. Undoubtedly that’s in part to the extra insulation, but the weather/heat load was probably lower, due to the cooler nights. I am convinced that it is quite efficient, and not that far from the 12 V units.
I've driven our van on quite a lot of rough and rocky roads, and the unit is still running fine. And my 6V batteries are still totally healthy after 5 years. So I'm happy with my choice, and have no issues.
Having said that, I'll most likely replace it with a 12 v unit if/when it dies. There are many more options now available than back then.