Recently got this to try and solve a grounding issue on a retro bass which I have never been able to get grounded (probably just the construction of its electronics). I also live in a house with lots of electronics even my grounded guitars have issues in certain rooms.
So out of hope, a wing and a prayer, I bought this. Had no idea if it would help was more wishful thinking that anything. Did it help?
Yes, not only did it help it was a wonder, no ground noise at all direct into my amp, and the tiniest hardly noticeable ground noise with my effects pedals and DI box plugged into the mains power.
The comparison without it is vast it is amazing the clean signal that comes through. Yes, it does impact the tone of the instrument but not much and if you didn't play it side by side you wouldn't notice. The tonal change is a slight cut of the mids and i mean slight. For me it is perfect actually, I like the deep thud tones on my P basses and this suits it really well.
Obviously I would rather not have one but its great.