I've used a "mercury magazine cap" on my Browning Gold Hunter for the past three years, and been very pleased with it.
My skeet scores improved (slightly) when I added it. In my case, the extra weight on the front end helps me swing-thru.
The recoil reduction is minor, and the same amount of lead might do just as well. Since the Browning is a gas-gun, recoil isn't all that bad with skeet loads.
The fact that the mercury weight comes as a magazine cap makes it easy to change back for hunting - although I seldom do so. The cap approach probably looks a bit better than a chunk of lead. I think I paid $55 for this device, from an outfit in Kansas.
I like this device, and think it helps my shooting.
