This sort of micro-fridges mostly use a couple of Peltier plates for cooling. Quite inefficient and energy-wasting, plus not powerful enough to really cool anything down. Well, they do work, if you need to cool a can of coke down to a drinkable temperature.
But when you mean business, beware.
I made an experiment with an aquarium chiller equipped with 2 x 45x45 mm Peltier plates. Ambient temperature was 31 (I live in Celsius world); test tank was only 5L of water (very well insulated tank). Chiller was set to 11C target temp. I started with 31C air, 31C water. In 5 hours the water was 20C, and did not go any cooler within the next 2 hours. I suppose if I needed to cool down 10 or 20L, it wouldn't go even that far.
Another experiment was with the same chiller, same tank capacity, same target temp, same ambient temp. However, now the water temp in the tank was 5C - very cold (same well insulated tank). My aim was to see whether the chiller would manage to at least keep the temp at 5C. Another fail. A day later, which is exactly 24 hours both in Fahrenheit and Celsius worlds, the water was at 19 degrees. It would in fact have been cooler had I not made it circulate between tank and chiller.
So, 10-11 degrees difference - well, may be. Real cooling - no, no way.
