I have the Megasquirt gold box and about 600 miles on my Hemi. The system is not the most user friendly, I have a pretty substantial amount of automotive expertise and electrical experience and think that. If you are very green to the whole idea of EFI, it is likely not your best choice. That being said, the only factory wiring I have on my car are the switches, everything else is completely new and/or modified.
It is, however, the most customizable. Which is what I wanted. I have basic traction control, the ability to expand to a %slip system relatively easy, I monitor many different parameters via my laptop and can do anything I want with it. I have plans to supercharge my engine down the road, I do not want to deal with any factory ECU hurdles or limitations with that.