I have one running on my Saturn. I have suspended operation until after the winter as I dont want to crack my cell.
I have seen up to 4 mpg increase with no other mods with about 1lpm. Unfortunately the CPU compensates as it sees a lean condition resulting from a better burn. The computer richens up the mixture over time and eventually negates the savings. I will be building an oxygen sensor output dial that will be adjustable. This will cause the CPU to stay at a certain fuel mixture.
The unit is completely home built for very cheap. I used 4" ABS plastic pipe for a cell case, stainless steal plates for electrodes and a bit of wire. I ran some gas into a plastic bag and lit it from a distance. It was VERY explosive.