We had a three-way fridge in our caravan. In the heat of summer - and I'm talking here:
the fridge couldn't keep up. With 45C outside, the fridge struggled to maintain about 10C inside. That night, it got down to 31C just before the sun rose!
The gas fridge is good if you have a decent gas supply. They are dangerous to use in gas mode while driving and downright stupid to use in gas mode inside a tent or vehicle other than where it is specifically vented properly.
They work by heating the liquid solution inside (usually an ammonia/water mix). Gas does this very well, with fairly low gas consumption. On 240V or 12V, they are very inefficient, as they have to basically become a heater, which really chews electrical power. They'll draw 10-15A on 12V, which is crazy - and since most of them only run the thermostat while on gas, the 12V setup will draw up to 15A all the time
What's worse: on 12V, because there's no thermostat, the fridge will eventually bring the internal temperature down as far as it is able to. If that means 30 degrees below ambient, it will freeze everything unless you're in the desert.
Some of them don't operate a thermostat on 240V either, so be careful - read the manual and make sure.