Good dan cong are not bitter. Bad ones are.
I would disagree - I think some good quality dancong and Fenghuang shuixian can be fairly bitter or astringent, or at least can become so if not brewed carefully. And, on the flip side, I've had some lower end ones that are fairly tolerant of strong brewing without becoming bitter or astringent.
I think one reason for this is that a lot of the higher end dancong can be a little less oxidized.
I had some beginners luck when I first started brewing it, but the more I drink tea, the more I believe the old story that this is one of the more difficult teas to brew well. What I find is that it's very hard to get the sweet spot of not too much "water taste", but also not too much astringency.
Some other great threads about brewing dancong on this forum, such as:viewtopic.php?f=3&t=7750viewtopic.php?f=3&t=10870