Depends on the advice. If they’re talking about their mistakes, that can be informative. But, if they discuss their mistakes and then say “… and this is what you should do, instead”, that’s just unproven speculation on their part.

But, at the end of the day, relationship advice is mostly useless, because only the most general advice works for everyone. The specific issues between two, complex people can’t be understood and advised for by listening to one side of the story for a few minutes.