Most chillers use a refrigerant and compressor to cool the water. It's the same technology that fridges and air conditioners user. The equipment is more expensive, but it's the most efficient technology out there and it can come in very large capacities.
Peltier technology uses semiconductors to create the cooling. It's a far cheaper technology, but it's less efficient and is only available in very small cooling capacities, which is why you don't see large fridges and AC units employing them. Only the smallest aquarium chillers use them. One other advantage is that the peltier devices themselves have no moving parts, so they have a theoretically unlimited lifetime, as opposed to compressors, all of which fail eventually. Peltier technology is what you see in those little desktop drink coolers, small countertop wine fridges, and the electronic coolers that run off a car's cigarette lighter.
Efficiency wise on the scale of a small chiller like this, it won't matter much.
In regards to the lifetime comment I made above, I should also mention that although the peltier device itself has a long lifetime, they are usually paired with cheap plastic computer type fans to dissipate the heat that have much shorter lifetimes than the compressor of fan found in more expensive chillers, so in the end, I'd expect the lifetime of the entire unit to be less. However, such fans are easily and cheaply replaced, even by a layperson with even basic electrical skills.
What price are you seeing on this thing?