I have the Diablo Predator and it is fine...I needed something to adjust for the oversize tire to get the speedo straightened out and it worked for that. I do like the firmer shifts, and withthe 87 octane tune I may have got back most of thepower I lost by going to a larger tire.
MPG = the exact same....overall power = same before the tire change.
I wnet with the hand held over the custom tune because I do a lot of towing and I tend to want or need to change setting occassionally....cannot do that with a custom tune. If I was pulling a 10000 pouont rv, I would go with a custom tune as most folks attest to the fact they offer better perforance.
The handheld units are fine, but they are generally somewhat universal....like buying a universal muffler hanger. It works ok for most trucks, but not really great for any...ha