Bushmaster offers them in their A2/A3 carbine line-up....Anyone out there have 1, or know how they shoot? Is it any better, or worse than the standard birdcage or Izzy flash suppressor?

Depends on what you mean by better or worse.  At reducing recoil?  Come on, it's a 5.56.  At reducing noise and blast?  No, and everybody to your sides will hate you on the firing line.

^  What I meant was in accuracy, & overall quality vs the birdcage & Izzy.  Would the AK brake really make alot more noise?

Not going to be much different than an A2 for accuracy.  In true precision terms (which you may or may not be able to appreciate depending on your skill level) brakes and comps degrade accuracy.  Not always, but usually.  There is a comp that has actually improved accuracy, but it was set up as the mounting unit for a suppressor, was quite expensive, and I'm not sure that they are even available outside of the .mil.
Not sure what you mean as far as quality.
Any brake that is designed to redirect the blast (and the izzys/AKs do) is sending it somewhere.  What would normally go downrange is now being directed to your sides and flanks.  Under something as simple as a tin roof on an outdoor firing range it can be painful, and shooters to your sides will not like you much.  The y-comp is one of the worst from what I hear, although I haven't been around somebody that uses one.

I've never seen the AK-74 style brake in action until some kid with his dad brought a SKS? to the stall next to me and proceeded to blast away with 7.62x39

The damn brake kept blowing powder in my direction and it seemed louder than normal. I fired my Vepr 7.62x39 and it wasn't nearly as loud or obnoxious in throwing powder/gas at the stall next to me.