I did this with my child. It is a large group and the kids have to be able to sit through a long class. I think it was 1.5 hours. I can't quite be sure because we did it the year before K. My child found it boring. There is also homework. I made my child do it. He did learn, but it was not enjoyable for him.
I would say it is not a great fit for a fidgety ADHD kid. It's best for a kid who likes to please and get praise for getting the right answer and raising their hand when prompted.