Using the Air 540 currently. First off as Kloaked said, too much plastic, though acceptable to me. Agree with him more on the inefficient space usage, as I believe more 3.5" drives could be fitted on the PSU side. Another downside for me is lack of dust filter for the PSU but could be easily solved by getting third party magnetic dust filter. It's also a matter of taste since not many people like the large footprint. Advantages would be the unobstructed airflow, ease of building in it, especially in terms of cable management because a noob like me could just stash away the cables and the system still looks clean in the end. The Enthoo Pro however wins in a lot of areas, mostly in terms of watercooling due to more radiator compatibility, bay reservoirs work better on the Enthoo Pro too since it uses standard orientation for the 5.25" bays instead of the Air 540's rotated one. In my opinion the Enthoo Pro also wins in terms of materials used. However do take a look at the Enthoo Pro M that will be released soon, at 79 USD if I am not mistaken mentioned by Hardware Canucks.