I first got into muzzle devices for my .223/5.56 AR15s as a way to allow my daughter (then 10, now 14) to enjoy range-time with me, when we're shooting the AR.
She dislikes the boomy concussion of the AR with traditional muzzle devices, and while I know that some brakes/comps can potentially exacerbate this trait, I also knew that there were similar devices out there that would shield the shooter, at the least, from blast/concussion.
My findings are pretty basic - virtually all of the "total surround" devices that fully trap spent gasses at the muzzle and direct it forward will work just fine for that purpose. Same goes for "linear comps."
There is, to some degree, a compromise in terms of recoil mitigation, but overall, it's really not much, as-demonstrated by Sage Dynamics' Aaron Cowan in the YouTube video below, withe the Griffin Armament M4SD/QD Blast Shield combo:
(go to time-point 2:35 or so, if this trait is all that you're interested in).
This said, the .223/5.56 really doesn't offer much recoil to begin with. Even my daughter, when she started shooting full-caliber ARs, understood this from our initial outing.
These work wonderfully well at shielding the shooter - and even adjacent shooters on the line - and directs both spent gasses and more of the muzzle noise downrange as well, but they do exact a price where it comes to weight. And as physics demands, weight further out on the end of that lever arm subjectively taxes the shooter even more. Items like the Surefire Warden and the AAC BlastOut, for instance, exact a heavy
toll.
On the other hand, variously "ported" devices like the Ferfrans CRD or the VG6 Cage fit over the underlying compatible muzzle device and aim to either mitigate the blast or more selectively redirect it - allowing the gun some level of muzzle climb/recoil mitigation at the same time as it allows for some measure of blast reduction/redirection for the shooter. On my daughter's AR, we've installed the VG6 Cage (on their Epsilon brake - we chose this combo because it's really rather featherweight), and it works really well to shield her from blast - meanwhile, depending on where I am standing next to her, I can either feel significant reduction, or rather little difference at all versus, say, a standard birdcage.
I haven't paid much attention at all to muzzle flash. I do run my Griffin M4SD/Blast Shield combo full-time on my gun, and I've taken several low-light classes with it, both outdoors on various flat-ranges as well as at a shoothouse facility where the only white-light came from that of our two-man team's WMLs. My understanding is that this will vary drastically depending on the muzzle device itself, and that while overriding "blast shields" or additionally ported devices such as the CRD/Cage may direct muzzle blast forward of the shooter, they can also at the same time redirect flash in these directions as well, and that because of the nature of the beast, the observed muzzle flash may actually be brighter.
TTAG did a fairly decent multi-part muzzle device comparison a while ago, IIRC, and it included both recoil mitigation (a straight-line measurement) as well as low-light flash comparison.
