I've had a couple of them in the past. It does cut down on muzzle flip, but it's more of a novelty than anything else IMO. That and those little holes tend to catch and build up plastic from the wad cups with heavy use, rendering them ineffective on top of being a b!tch to clean.
Save your money, and look for a ported barrel on the used rack at the LGS if you want to try it out at some point. I have seen ported M 500 or 870 barrels at my LGS for less than the cost of having it done by a smith.
If it ain't got papers, deport it.
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I may live in the North, but I still uphold Southern Values.
lifetime member. NAHC, NRA, And SCOPE NY