I've written about this extensively in the past, and I'm not interested in arguing about it. Unlike nearly everyone else with an opinion in this thread, I've used the thing, I thought it worked, and I'm chomping at the bit for them to get something to market.
My subjective ratings for distress and volume plummeted after 2 weeks of using the device, and rebounded back to baseline within a week of the trial being over. I don't have access to the data about the objective volume measurement that they did during the study, so I can't tell you if it "really lowered the volume".
I've also had tinnitus for a long time, and I personally do not need silence/"a total cure"/etc to be happier and more functional. My tinnitus never really seems to change in volume, exactly, it's a question of to what extent it's passive background and to what extent it's piercing/painful/very foreground data. The latter two weeks of the trial, the noise was comfortably doing a quiet thing in the back of my mind, and I suspect that if that was my baseline, I would quickly stop regarding this as any kind of problem. 20 years in, a constant tape hiss does not seem like a problem to me; a piercing/stabbing/physically uncomfortable jab in my ear definitely does. That's the spectrum of my tinnitus, and I can not with certainty say there is a difference in "volume" from one extreme to the other.
If you're in the absolutest camp who demands an absolute return to silence before we can say "success", then you will need to look elsewhere.
I am sorry if I am being combative; I am extremely tired, hundreds of miles from my home my wife and my kid, and pretty much every time I login here I end up getting drawn into something that makes me regret it.