In reply to greg_may_:
I've obviously not been there for a few years but it used to be bad, chest height type stuff but if you got on the right trod it was OK. At least you are going up hill through the stuff. It's certainly worth recceing that section.
I did the Beddgel Parish Bounds years ago which came down Foel Ddu (I think its called - further west than Bryn Banog), it was a large gully filled with chest high bracken and you couldn't see anything and they were snagging your feet.