The SIMS/Limbsaver De-resonator has been around for about 10-12 years... I think. Like a lot of barrel harmonic devices, it actually works on some rifles... and does nothing at all, or just the opposite on others. The most consistently
successful harmonic devices are those frequently found on target and BR50 .22LR benchrest rifles.
If you don't mind me being really
general in my observations, it seems to be that the larger and faster the caliber, the less effect it has. That statement is not 100% accurate however as I've seen one mounted to a Remington actioned, .220 Swift varmint rifle and it actually had the effect of cutting groups nearly in half... and on another Remy .220 Swift on the same day with the same ammo, it did nothing at all.
It'd be interesting to do a multi-caliber, big sample, controlled test on the thing, wouldn't it?
As they are not terribly expensive and you can play with them on just about any rifle (they're are only two sizes as I recall)... might as well try it out before you automatically toss them in the useless gimmick pile.