I've been running the Manticore Arms NightBrake for a while and here's what I've found:
Pros:
-Very good muzzle control during rapid fire strings.
-Reduces perceived recoil
-Reduces muzzle climb
-No ports face directly upward to prevent the muzzle flash from getting in your sight picture when firing in low light.
-No ports on bottom 90 degrees to prevent dust from coming up in your face when firing from the prone.
-Machined 8620 bar stock with a "deep black oxide" finish.
-Crush washer included (it just annoys me when they're not...)
-Can be used on ARs (and other 1/2x28 threaded rifles) firing up to 30 caliber (.311'' clearance)
-Cost. Can be picked up for around $50
Cons:
-Slightly increases muzzle flash. Not as bad as some but more than the A2 or Battlecomp for example...
-Slightly more blast than an A2 flash hider. Nowhere near as bad as a side port style brake however.
All in all, it's a very effective brake; especially for what they cost.
Here's a video with some day and night shooting, a discussion of specs and my overall thoughts on the brake:
Manticore Arms NightBrake HD Video Review Link