Six reformers means six people. The margin depends on those places being filled, and a waiting list that automatically offers a cancellation is worth more here than in any drop-in class.
Conditions have to travel with the booking. An instructor covering a class needs to know who is postnatal, who has a disc problem and who was referred, because a modification not made is an injury waiting to happen.
Not every instructor can teach every class. Equipment, prenatal and clinical work require specific qualifications, and a cover arrangement has to check that rather than assume it.
Blocks and memberships expire differently. A ten-class block with an end date and a rolling monthly membership need separate handling, and clients notice immediately when one is billed like the other.