I have never driven a model steam locomotive so I hope that the experienced drivers will excuse this question. I have noticed that many of the 3 1/2" gauge engines have optional manual brake designs. Are they more of a cosmetic addition at this scale or an important feature?
Phil, the brake designs you will see are usually for appearance sake on the smaller engines, and used as a parking brake. you cannot get them on fast enough while running. In operation your real brake will be on the driving trolley.
This is true in full size practice too…the engine starts the train and the train stops the engine, as my father used to say. (except for those horrible unbraked four wheel wagons the British used to use on goods trains!)