I went to see it a couple of weeks ago, about a week before the end of the tryout run in Manchester (I live about ten miles from Manchester city centre). I have to say I went with very low expectations, and mostly because of the cast - the Max Martin oeuvre really isn't my sort of music - and I was bowled over by it. It's an absolute delight - smartly written, VERY funny, and hugely entertaining. It's enormous fun, the performances are superb (all of them, but particularly Miriam-Teak Lee and Cassidy Janson), and it deserves to be a great big hit.
They've put out a trailer this week, and it gives a reasonable sense of what the show looks like and the idea that drives the plot, but it doesn't communicate how funny it is (see link below).