The thing I’ll say about them (and I’ve been using for a year) … and I’m not sure if the super speed guys would agree or not … is that after using them, don’t TRY to swing harder on the course. Just swing. Your swing should be faster but not because you feel like you’re giving it everything in the tank. Yes, if you’re on the range and try to go after it you probably will hit it even further - but if that’s not normal for you, don’t do it right away.
When I first started, I went to the range and was swinging out of my shoes. It was going further and pretty straight, but then I couldn’t translate it to the course. On the course with a “normal” swing it was still going farther.
The level of effort can certainly be racheted up over time as you get more speed and control over it.