Do hydrogen generators improve gas mileage?

In my experience, yes they do but there's some things to keep in mind. My experience: It worked great at first but required some automotive knowledge to install. After running my generator a month or so, it got all gummed up and i had to take it out and rinse it off and clean off the plates. I had to add water to it and some powder to help the HHO gas production every few fill ups. More maintenance than i thought was worth it.

I no longer use it, I use a fuel catalyst called Fuel Infusion - www.fuelinfusion.com. It's much easier, i just add a tablet to my fuel tank every time i fill up. I did have to "flash" my computer after I first started using it (take off the negative battery terminal and turn on my lights for a few hours) but that was just so that my car would see the results quicker. I see about a 10-15% increase with it.

Hope that helps.