I think the above poster has some bias against the Ariakon company, due to his experience with the product he received from someone that is not a licensed dealer of Ariakon products. I am an owner of an Ariakon ACP 2.0. It is a pretty decent pistol, but it isn't the higher end pistol that Ariakon makes, the Overlord is. Aside from that, the ACP 2.0 is accurate, and not all that bad. The ACP cannot be customized easily with what you are given, you have to alter the actual marker in order to customize it the way you want. The Overlord, on the other hand, is much more custom friendly, and from what I hear, it can share custom parts made for other paintball pistols. The spare magazines (or clips, if you will) are not compatible for both markers, the ACP 2.0 clips work only for the ACP 2.0, and same goes for the Overlord. As far as I know, neither markers have a top rail system because this is where the magazine attaches to the marker (there is not clip in grip option). Although I am saying this, the Ariakon products are pretty decent choices for paintball pistols.
Hope this helps.