It took them three albums to get there, but The Saturdays have finally refined their signature sound, a lethal mix of ‘90s club beats and intensely sweet melodies that build up to excessively banging climaxes. ‘30 Days’ isn’t quite as memorable as the glitchy ‘Notorious’ or sweat-doused floor filler ‘All Fired Up’, but it’s a perfectly danceable addition to their rapidly growing catalogue of girlish dance pop.