Good find. I've been more than happy with my G-Power Z4M. The ASA supercharger is the best centrifugal unit out there in terms of performance. It's lighter and more efficient than a Vortech, but more expensive to maintain in terms of rebuild costs. I wouldn't be put off by 306 bhp. It is similar to the VF kit in terms of boost pressure, and it will likely have more midrange power but less top end.
Personally, I would rate this kit above other non-intercooled centrifugal kits but below the ESS twin screw kits, assuming you don't intend to swap pulleys to adjust boost on the kit. G-Power kits are packaged as the end-all of kits, so they do not expect you to increase the boost and modify the kit. My M kit has zero headroom. Other kits are pieced together with some custom parts, and they typically include oversized superchargers, which is why I was able to modify my non-M's VF kit for higher boost.
Bottom line - great conservative kit that will put a non-M in the same power league as an M. You shouldn't really go much further on an M54 anyway without serious work, but if you want a high boost build, you need to go with a twin screw or Vortech unit.
