This is without a doubt one of the worst products ever made for a game system. It is incredibly dangerous, and can destroy your Xbox 360 randomly. In my experience of it, after a while of gaming, the 3 red lights appeared on the console and we could smell smoke. The unit had failed and was about to catch fire.
The product has a good idea behind it, but fails woefully. Drawing Power from the mains means the electricity actually running into the system is reduced, so the Internal Fans run slower. Now, the Intercooler is designed to refresh the air circulating inside the case, but has no effect on the heat the processors run at. As you can imagine, less internal fan speed means it runs hotter meaning... bang. A certified Explosive 360.
Nyko have gained a bad reputation for releasing terrible products which seem to have passed no safety checks whatsoever, and are incredibly dangerous. Take this warning Xbox users. Microsoft have seen the damage these awful things have done, and now if you use one of these Nyko devices, your warranty is voided.
In short, the Intercooler doesn't work and only contributes to the overheating of the system. To put it technically, you'll be paying out £270 in the end (£250 for a 360 Premium, £20 for this horror of horrors) and only get some cheap smoke effects out of it. Not good at all.