I have the Bully Dog. I picked it up from AutoAnything for just over $400. It was out first and had the gains I wanted. I also figured if the Diablo was that much better I had 30 days to return it. The $475 above from Hemifever, with his tune is the way to go if I was to to it right now. I thought he was at $599 with a tune. I have very mild mods and except for setting my e-fan temps, don't see much need to go through the aggravation at this point and spend more money. I also don't intend to do heads/cam/headers but if I do I'll sell my BD and get the Diablo and custom tune.
Hope this helps!