The problem is that you're limited in the 24V arena for good products that are mileage oriented, the reason is timing. The VP44's control the timing of the injection pulse (to a point) and they are timed (mechanically) by way of the key in the pump gear. You can only modify the timing so much in VP truck because of the design of the injectors. They require cylinder pressure to open, so adjusting the timing of them is tough. You can program in all the timing you want, but the injector won't open on a VP truck until there is sufficient cylinder pressure.
If the Smarty Jr was available for the VP powered trucks, that would be my first choice, but it's not and an S03 would be more than he needs for what is being talked about. Having the ability to adjust / modify the timing is where you make money in the mileage department. But think about it..... at 1 - 2 MPG increase (max), $649 will take a while to pay off. Same thing with the Adrenaline w/ Pulse. 1 - it's been quirky (to say the least) and, 2 - it's a $700 (w/o Pulse, $900 w/ Pulse) unit that has one setting with Max Mileage tune. That's a lot of coin for "hopeful" mileage increase.
My next choice would be the Edge Mileage Max. It's a timing / pressure module, only adds 35 HP, doesn't "really" need a gauge package to run it, and it's a 10 min install.
After that, I'd say the Quad. It's similar to the Edge, easy install, and almost identical results.
NONE of them, except the Smarty Jr (which isn't available fr this application) are, or have been, without issues. Edge has had problems with boxes overheating, Quad has has problems with harnesses and programming quirks.
In the customer service area, I have to give the nod to Edge. I haven't had an issue with them, so in this case my recommendation is the Edge Mileage Max.