Depending on where your laptop's fans, hard drives, and graphics hardware are located within the chassis, an external cooling fan could be more useful in some positions than others. Being able to position the fans within the Cryo E40 lets you put them to use where they can do the most good.
The E40 is designed for laptops up to 15 inches, which is a shame, as it'll be the bigger 17-inch desktop-replacement models that could use the most extra cooling. Fortunately, I had the just-reviewed on hand. With a third-generation quad-core Intel Core i7 CPU and Nvidia's new GeForce 675M GPU, it packs a lot of heat-generating hardware into a compact case.
After Ion the Maingear without the lapdesk in place, the hottest point on the bottom surface of the laptop hit 120 degrees Fahrenheit, as measured with an infrared temperature gun. After placing the laptop on top of the Cryo E40, moving the fans to cool the rear of the bottom panel, and gaming for an additional 20 minutes, I found the temperature in the same spot was 103 degrees. That's still pretty hot, but the NZXT Cryo E40 (like any lapdesk) also serves to keep the actual laptop surface away from you.
I did run into a couple of snags with the system. The fans needed to be placed carefully, and moving them too close to the front edge led to rattling, as the lapdesk interior isn't high enough at the very bottom part to fit the fans. A couple of metal screws on the inside of the top panel also prevented me from moving the fans as freely as I wanted to, and the coiled USB cable connected to both fans (which can be led out to your laptop via an access port on either the left or right side), was stiff and a little unwieldy. It has to be to positioned carefully to both avoid rattling and leave you enough room to reach a USB port on your laptop.
Despite those issues, the Cryo E40 is compact and portable, its matte-black finish and metal construction give it a sophisticated look and feel (especially for the price), and it manages to do something just a little different than other lapdesks and laptop coolers do.