The patent mentioned seems to be US 7,191,737, which can be seen at
United States Patent: 7191737
It looks to me like a rather primitive device for electrolyzing water. The news releases make a big deal of a "new" gas, HHO, without explaining how this is different from everyday H(sub2)O, or water. Maybe it's that Klein leaves the electrolyzed hydrogen and oxygen mixed together, as seems to be described in the patent. In that case he perhaps means HHO to be a simple mixture of atomic hydrogen and atomic oxygen. If it's important that they be atomic rather than molecular (that is, ordinary H(sub2) and O(sub2)), the patent doesn't mention it.
In other words - sounds fishy to me.