Seems like a weird gizmo contraption, it's smaller than I thought, actually quite discreet on a headstock. I was curious about the physics behind it, which seemed to make sense, and they do.
Now, you won't notice an improvement in your tone, your playing, your hairstyle... in fact you pretty much won't notice anything, except all of a sudden, after a jam session, you'll think, jeez, my guitar is still in tune.
This is what you would or should expect from this kind of technology, to do the job quietly and discreetly so you forget it's even there, except that you have one less problem.
Before you get this though, check that your nut slots are not cut at an angle instead of straight, which some brands will do to try and fix the "G string curse", because this will work against the butler and actually make things worse unless of course you change the nut.