it's a combo but general consensus that it's treated as break.
it exhibits all the attributes of a break: as forward pressure surfaces, gas discharge side vents and top vents. it lacks that distinctive open front internal cone shape and coaxial slits that's very characteristic of flash-hiders.
Well it's called a brake but who knows what MA considers it. I have one on my 74 and bought one for my 47 and they work well. Here's a neat video comparing a 47 with no device as compared to the slant and 74 style. http://www.youtube.com/watch?v=ZbGixCAb0B8