I run the accel DFI system on my challenger and am very happy with it. Mine is a batch port system running a wide band closed loop. However, I wouldn't plan on saving money with it. A very well setup carb will get you good mileage and can make just as much power with a properly setup carb. The advantage of the efi is the way it can adapt to different situations. i.e. you can set your carb up for great economy, or you can set it up for great power, but its very very very hard to come up with a setup to do both. The efi can do both.

I believe the mileage gain in hot rod, and I think the FAST setup looks like a good product, however the mileage results they got are not what you should expect if you are currently running a well calibrated carb.

If mileage and driveability are your goals I would start with a overdrive tranny first, and then consider efi.

-Jon