You can see why, having quit as an SNP MP after nine years in parliament, Mhairi Black’s first move is on to the standup stage. Goodness me, she has a story to tell! No one else’s 20s were quite like this – from becoming our youngest MP since the 1832 Reform Act, at the height of the independence surge, via the party’s deputy leadership in Westminster amid battles with fellow Nats, to retirement aged 29 as the SNP’s support plunged. After all this, autobiographical bantz from a comedy stage must seem a breeze – although not everyone has given up on her political career. “Mhairi for PM!” one audience member bellows, before Black has even made her way to the microphone. “Nae pressure, man,” she responds, grinning – and if this foray into performance proves anything, it’s Black’s popular touch and ease with an audience. This isn’t standup, she tells us, it’s live therapy – but if it were standup, I don’t doubt she could pull it off. The therapy is required after a bruising decade in Westminster, whose culture and archaic rules are crying out for reform. The show opens with snaps from the Black family album, outlining a background in stark contrast to, say, Eton College – which Mhairi visits and on which, as she demonstrates, parliament seems explicitly modelled. This first half is irreverent and self-unserious, as our host laughs off online abuse and gets potty-mouthed in parliament. She keeps scuttlebutt and score-settling to a minimum, at least until the end. Before then, the show devolves into a public information seminar, as Black talks us (with diagrams) through House of Commons protocol: the “prayer cards”, the division bells, hiding in the toilets to delay a vote on Gaza. The combination of inefficiency and flummery (what’s with all the swords?) draws gasps from the audience, even if this section is less sparky than the earlier personal material. That’ll be fine with Black: with her agenda to encourage public participation in government, you sense she’s not done with politics yet. In the meantime, this is a winning stage debut that persuades you “Mhairi for PM!” might not be such a bad idea. At Gilded Balloon at the Museum, Edinburgh, until 25 August All our Edinburgh festival reviews