Mine hasn't arrived yet, but from reading it seems most describe the NFB-11 as having a neutral bright sound. I understand the Beyerdynamics to be fairly bright uptop , so depending on you taste you my find it a bit on the bright side.
I have no personal experience, just relaying what I have read and how I understand it.
I think the NFB-11 is neutral.
You often here the description of it as "bright" in comparison to the NFB-15, which had a bit warmer sound. This, I think, has propagated the idea that the NFB-11 is bright, which I don't agree with. But just my personal opinion.