Kinda depends on how its used.
Many times such "clubs" are used to reduce "churn" or people quiting the school--if you can get them in a "black belt club" you stand a better chance of them sticking with training ie longer term student ie more $$$$$$$$-----at least that is the theory.
That your guys don't chage a penny for it is a really GOOD sign BTW.
As such "clubs" also often serve as another way to generate revenue.
Many such clubs have you buy "special" patchs/uniforms/belts etc as a sign that they are in such a "club."
Club members often get asked to attend "special" seminars that are "closed" to non-members---with a fee involved of course
Sometimes they are allowed to start weapons training---with the weapons needing to be purchased from the school.
Sometimes they spin the whole "leadership" angle on the "black belt club" and tell proseptive members ESP the parents,that such clubs teach "leadership" skills---which is all to often code for "were going to make you work for us for free while you pay us for training."
"Extra classes"--bascially the cost to an owner month to month is a sunk/fixed cost--its going to cost them the basically same if the doors are open every day of not.
(sure the extra hours of lights/heat/ac whatever are going to cost "more" but usually not that much.)
Such "extra" black belt club classes are a cheap way to get more use out of the the fixed costs.
Plus, presuming that classes are in some fashion visable to the public---can be really good advertising.
A buddy of mine let an aikido group use his school on Sundays for nearly free---just a "mat fee" and he had to be added to his insurence policy-the extra cost paid for by the aikido teacher.
Only asked 2 things.
1-That HIS students be allowed to cross train in aikido for a reduced cost.
Any NEW students the aikido guy picked up would have to pay a little more then the group he brought in with him.
2-If anybody came in to see what was going on---that the teacher got their names/contact info so he could call them and see if they wanted to come by and check out clasess in general.
Guy came up with a nearly free way to get some revenue generating use out of a building that was just sitting their empty anyway.
Anytime the doors are closed--your losing potential revenue.
I think its a good plan BTW--nothing at all wrong with it.
BTW don't mean to sound so cynical----but as I am---why fight it????
Again, that sound like 180 degrees from what your school is like.