I put one in mine, very nice kit.
the truck had a bit more power, no savings on fuel, but with a mechanical fuel pump, that would be expected.
without a dyno to prove the power increase, then being able to turn down the fuel pump to decrease full delivery, all the while monitoring head temp, there would be little benefit to the upgrade. also the generator puts out a static volume of hydrogen, so the gains would be seen primarily in the low end, with potential sacrifice in the high.
as I said though, there seemed to be a bit of a gain in power, but without access to a dyno that can fit dual rear wheels and read the rpms of an old diesel, it is all here say.
this can be a touchy topic for some.
this reply is not meant to be a final authoritative statement on the topic, but rather a short summary of my personal experience and findings to my specific experience with this specific setup and vehicle.