I run a reflashed factory Magnum JTEK computer that has been reflashed on my 408" Magnum. I had a guy on the east coast tune my set-up. It took 3 tunes to dial it in. It was a simple process and it works very well. I did use the Hotwire Auto Hotrod harness, which made the install plug and play.
When I get ready to supercharge my next build, I'll switch over to the Holley Terminator ECU. The reviews, flexibility and added functionality it offers are attractive. The self-learning and tuneability are said to be second to none.
My buddy runs the Proflo 4 on his RB. It's been everything they said it would be. His car runs great.