Look at Australian systems. It's been popular down there. The good ones have sensors and proportional mix.
Gives a better combustion of the diesel and a longer power stroke. Less soot and pollution as well as the combustion is more complete. As the power stroke is longer and smoother, it gives a lower peak stress on the moving parts in the engine, even if you get a higher overall output.
I would have installed it long time ago if it wasn't for the regulations for having a gas tank in a vehicle. It has to be installed and certified by an approved company, and they know how to charge for their monopoly, at least around here.
PS
Isn't it called gas fumigation? And it's propane or LPG.