Blackout "tings" like a tuning fork without the can installed. Blackout is a phenomenal flash hider. Works GREAT. Nearly no flash with a 5.56, .300BLK or 6.5G. Not bad with a 7.62 either. I was surprised. Brakeout on 5.56 is like this: it's a jack of all trades. It has decent braking ability, not the best, and it has decent flash suppression, not the best. The brake negates some of the flash suppression and the flash hider takes up what would be the second chamber of a good brake. I'd say it works as well as a mediocre brake and as well as a regular milspec or other flash hider. So all in all, it does both jobs about as well as either a mediocre flash hider or muzzle brake, but not great at either. I can see it helping save the can some, but with an Inconel blast baffle, I can't see how you'd need much, even with a short barrel. With a 5.56, it doesn't do much as far as braking, and the flash hider works just well enough not to bloom NODs too much.
The flash hider, again, makes a tinging noise but it does negate much of the flash to the point NODs don't bloom. It's pretty efficient.
I'd personally either get the flash hider for a great flash hider or their brake if you wanted a decent brake or wanted to minimize any damage a short barrel might do to the can's blast baffle. I got the brakeout because my wife picked up a part for me on hold and they had the wrong part --the names are easily confused. I kept it because it was so far away and I was interested as I have 5 other blackout's. Interesting, but not my first choice. On the other hand, if you do want a jack of all trades and superior flash suppression or superior braking isn't of issue, maybe it's not a bad idea. It does work as advertised, it just doesn't excel at either.
Be prepared to grind/lap/turn the mount, whatever you get, in order for the SDN-6 to fit properly or else it'll "wiggle" and you can have a baffle or end cap strike. If you have the opportunity, if you haven't ordered the SDN-6 yet, consider a different can that uses a different mount. AAC makes a great can out of the best material, but they haven't figured out the QD mount yet.
Elite Iron makes a great looking mount I haven't tried (threads on the barrel, the can threads on the mount) and then there are others too. But if you have the SDN-6 on order, research the methods on here and be prepared to fix the mounts because AAC is aware of the problem but doesn't really care. However, once fixed, the mounts lock up nice and tight and square, and the can works great with little to no impact shift. Good luck.