Well, the most effective flash hiders would appear to be the three or four prong open models.
If I recall, the US military uses that flash hider design on the Mark 14, and the FN SCAR 17, both of which
are frequently suppressed.
I was curious about the use of a cut down MP7 FH on a very short barreled AUG. The MP7 has a
considerable difference in it's blast characteristics as it is a 4.7mm PDW round. My concern would
be how well that particular Flash Hider will hold up under under a 5.56mm blast from a AUG 14" barrel.
I think as general rule, most major sound suppressor manufacturers carefully mate their suppressors to an appropriate
flash hider and Surefire, AAC and Smith Enterprises all use open prong designs for their government production.
Just some food for thought.