Narrow gauge railroading is almost always confusing, and On3 vs On30 is no exception. They sound similar, and they are, though there are some differences.
Narrow gauge has a following among hobbyists who want to be able to model small areas accurately. Most basements don’t have adequate space to model a big-name railroad with any kind of scale accuracy. But it’s possible to model a small narrow gauge operation in a small space. Narrow gauge O scale trains are a great compromise for people who want big trains in a small space.