I think it's great, to be honest. Obviously, you have to filter the 'advice', but it's a very healthy place.
My exH and I found out something about my mother a couple of years ago and we were absolutely stunned. We couldn't seek advice IRL because the law prevented us from talking to anyone about it.
Some of the advice was better than others, we were advised by people who were professionally experienced in the field on here and made the decision to go NC. We wouldn't have had that experience IRL.
Similarly, when I discovered my exH had been on NSA sites. I received a tremendous amount of support on here. Complete strangers told me what would be revealed next, I reassured them that, as much as I appreciated their good intentions and support, my husband wasn't "like that". Guess what? He was just like that.
The difference is that on MN you benefit from the collective advice of people who have been through similar, who work in that field, who recognise the signs, who have seen it all before... in my personal life, I get very different advice. Some of it I trust, but I have to say, that when it comes to the tough messages, MN is actually more reliable and trustworthy for me, simply because people are speaking from personal experience of similar.
Yes, some people project and some people do appear to be playing an online game, as someone suggested earlier, but you get to know the names you trust and the advice you value.
And it's free from the patriarchal misogyny that most of us experience in daily life, even in the advice of well meaning friends.