I bought one thinking that it might help with a flinch I was struggling with. A flinch might be a result of recoil reaction but in reality most flinching problems have to do with riding the target and/or trying to aim with the bead. In other words it is between your ears. Now as far as recoil reduction - I shoot the same scores with or without the mercury reducer.
If you want to buy mine let me know. There are at least three styles. One for an O/U fits in the chamber( this is the style I have), one for the magazine for use in pumps or Autos, and one that fits in the stock bolt hole. If recoil reduction is your intended use try a gas operated semi plus a good recoil pad.