I tried a couple on my rimfire benchrest rifle and they seemed to work, but not as well as a weighted tuner near the muzzle.
There was a test that compared extremely large-diameter rimfire benchrest barrels, vs smaller-diameter barrels with tuners and the ones with tuners that were properly-adjusted shot better. Many people use 10.5 lb rifles with tuners for both that class, and the 13 lb and Unlimited classes...and win!
People are like rifles. Some are tried and true, having great eyes, personality, and fun to be with. Others never seem to hit the mark with you. Still others go off half-cocked. Still, it's nice to know most of them.