What track cleaning fluid should I use?
This detailed article by Joe Fugate in the May 2019 issue of Model Railroad Hobbyist Magazine
should answer all your questions:
Why are there different models for N, HO and S gauge?
When Centerline Products first started, we offered the cast brass rail cleaners with "pointed ends". These cars are not designed to NMRA specs for width.
Later, we developed N, HO and S gauge cars designed to NMRA specifications. These rectangular cars were originally die-cast zinc and painted black. You could kit bash a boxcar, caboose, etc to cover one of these if you would like to disguise it.
In 2015 we purchased a HAAS VF2 CNC mill. At that point we started to machine the NMRA specification bodies from A360 brass bar. This purchase allowed us to made all of our track cleaners in brass at a similar production cost. An added value for the customer as compared to the original die-cast. But, now that they are all brass there is some confusion... "Which works better?" is a question we are often asked. The NMRA spec cars use a slightly wider brass roller. They all will clean in a similar manner. But, some customers prefer one over the other.