Not sure which one you are talking about. you didn't post a link.
I did test a "Hyper Voltage Systems" voltage regulator that just connected to the battery and I gained 3hp. I didn't think it would work, and I was shocked to see a gain. But, I did it at a dyno meet with about 20 witnessess.
You want my opinion. Its not worth it for a 0-3hp gain. No matter how cheap it is. Because your not going to feel it. You're not going to be fast, not matter what you do to that car, unless its Turbo upgrade.