THEY ARE FANTASTIC!!! I have one on my SU 16, and thought it wouldn't make much difference as I assumed the muzzle jump was mostly from the heavy op rod cycling above the barrel.
NOT SO! It moves about 3 to 5 moa between shots now! Before, it jumped so much, my target would be out of my scope's sight picture between shots. Super can killing modification!
It directs all the noise forward, cuts down on recoil very noticeably, cuts dramatically on dust firing prone, protects my spotter, I can't say enough about it. I ABSOLUTELY LOVE MINE. It will NOT be a paperweight. I don't entirely understand how they work, as the gasses are still directed forward, but the way I (sort of) understand it, is that the gasses are dispersed into 7 ports behind the bullet, thus cutting down on their velocity. Hence the velocity of the gas is less as it leaves the compensator.
The skinny of it is that on my SU it works FAR beyond my expectations. I would absolutely put one on my mini except they aren't available in stainless. The finish might look a little funny on a blued rifle, too, as it is phosphate looking, like an AR barrel.
That "grenade launcher" thing is a sack of it. Mine is 23.37mm in diameter, and doesn't have the necessary ribs. I heard that a while back and went looking to find out if it was illegal. I didn't get a response from the manufacturer, but got a card from my local sheriffs dept. to vouch that I had checked it out. The deputy I spoke to said I probably didn't need to worry (a deputy is not a lawyer).