I have the CX30 (only one that will fit under my tonneau). It isn't perfect, but honestly it does a good job, especially for the price. I haven't tried another 12V fridge so I can't compare but my only real complaint is the temperature gradient inside the machine. Directly below the compressor is the coldest area but it gets progressively warmer up towards the top. You can use this to your advantage if you're smart about it, but overall it's just kind of annoying. I set it to about 32F and place meat directly below and cans on the bottom to the side then everything else I pile on top. The meat will be very cold (sometimes even semi-frozen) and the cans will be quite cold. Stuff on top takes quite a while to get close to the same temps below. For example a can on bottom will get to ~35-38F in a matter of hours, but a can on top could take 6+ to get in the low 40s.
All told, I'm still happy with it for the price. I'm actually considering purchasing a CX50 while they're on sale now that I'm swapping out my tonneau for a cap. $270 is incredibly hard to beat for 50L of storage.
Also, they are advertised as having LG compressors. Some people have left reviews saying they are branded differently, and still others claim they called the company and the company stated those are in fact LG compressors but can't be branded as such. Idk, but they definitely get the job done.