My dd has been going to a class on Saturday mornings since Sept 12. its 45 mins per class (£10) but badly organised so there is no breathing space between one class finishing and the next starting, so in reality she probably only gets 35 mins. I send her as a fun activity to do, not because I want her to be involved in the entertainment activity. She seems to enjoy it, when she no longer does we will withdraw her. My other criticism would be that we cant see what the kids are doing as there are no 'portholes' in the windows. I don't know if this is to prevent distraction by parents. Although they did do a really cute Xmas performance so the obviously learn something.
There is also Stagecoach which is held on sat mornings at Highfield prep school but much longer classes.