I think the concept is good. Particularly because I think there is such a wealth of humour and information in some threads, that it seems a waste that they are just left to float in the cyber ether once they're finished. And after all, every other media outlet seems to be exploiting the threads, so good that MNHQ are "taking back control" as it were. (As a passionate Remainer, I never thought I would be using that phrase in a positive way! 
). Anyway ... .
I definitely liked the way the presenters were respectful about posters and content, and didn't mention specific nns.
Overall I quite liked it. I wasn't blown away but it was fine to listen to while doing something else if that doesn't sound too impolite! Not as good as "Fortunately" but there again Fi and Jane are radio goddesses.
Sometimes I felt that the amount of laughter being generated was not justified by the content. It was if the producer (director?) had given instructions such as "remember now you must all be a bit giddy". The laughter had to be genuine or it becomes irritating.
Lucy Porter is a real find. Fantastic. And she and AM are able to go off on interesting tangents which is good.
I disagree that it needs to be longer. A good podcast leaves you wanting more.
Also, I think the "celebrity" input is fine. The programme needs to have a focus and that provides it. I'm not sure having ordinary mumsnetters on would work in the current context. But maybe at some point you could invite a selection mumsnetters to discuss certain topics and record/edit the best exchanges/contributions and then include that in the broadcast?
Agree about needing to widen content beyond AIBU. Classics a good start. But how about topics that aren't really topics ifyswim and are more "Mnsnet themes"; CFs, parking, how often do you really wash bedclothes, the Mumsnet chicken that goes on giving, that sort of thing?
Overall 6/10! Keep going!