Tom and I have had to deal with this a lot in our counter-supply business. Counter customers who want to order a right-hand mount counter ask us if it will fit. We tell them we don’t know. It depends on the diameter of the hub flange. The most common flange has a diameter of about 2 inches, and this is the diameter that the counter is designed for. If the flange has a bigger diameter, some cobbling by the owner may be necessary.
The presence of the brake disk assembly is generally on the left hand side of the wheel as it’s ridden, and has no effect on counter operation.
As much as we would like to have a one-size-fits-all counter, it’s just not feasible, so we aimed for the most common hub size.
We have suggested purchasing a cheap front wheel with a 2 inch hub, and using it as the wheel of choice while measuring. I have not heard yet that anyone has done this. Considering that riding speed should not exceed 15 mph, the lack of a front brake is not much of problem. I never used my front brake while measuring anyway.