Yeah, I used one on a pesky, too thin, barrel I had put on a 358. I think it helped, but I've since just cut down the barrel to 18 to stiffen it up and that worked better.
Beware not to leave it on for long in the safe after you have it out in damp air or rain as it holds water against the barrel. Also, you have to then make sure you put it back to the exact spot it was in when you sighted in the rifle.
One would think gimmick right off the bat, but I would think you could probably play with the placement one the barrel to change the harmonics. It could act like a poor man's tuner. Simply put a cheap Boss system like browning introduced years ago. Technically speaking you should be able to move it back and forth on the barrel and find a sweet spot, will it be noticeable on a factory gun, who knows?