Review on High-Performance TEC1 12706 Heatsink Semiconductor Refrigeration: Effective Thermal Management for Industrial Electrical Applications by Travis Caminiti

That's the problem with them and if you're trying to get as cold/warm as possible you have to consider this: The highest current I could draw with one of them at Starting (without thermal gradient) is 4.2A at 12V assuming a go to 5A. This varies from slab to slab and there is almost never the same force on any one of the slabs. The reason for this is that the temperature gradient isn't as high on either side of the plate when not drawing as much current, meaning you don't get really high or low temperatures. It's a good buy if you want to stay at reasonable temperatures, but if you're really trying to cook or freeze something it may not be the temperature you want, it will vary and that's just due to the manufacturing process. Keep in mind that I've tried several tablets from different places and almost all of the ones I've tried have the same history and different power consumption, so it might be as good a buy as any.