Can I save money by adding hho to my 1990 ford ranger?

I always see these water generators online that claim if you add this to your already fuel burning vehicle it would make it more efficient. I love my little ranger but gas is so expensive and I drive long distances. It just doesn't seem like it could actually work or more people would be doing it right? Are the kits hard to put in? Is it worth my time/money? Will I actually save or is this just what they are claiming?

Hydrogyn fuel cells? I tried that as did my friends and they don't do squat for fuel milage