What you want from a secondary source is a good introduction to a concept, that is mostly reliable, up-to-date, entries for as many topics as possible, connections to where to go to learn more, and easy and ubiquitous (as possible) access. A secondary source is not an in depth analysis which upon reading one is suddenly an expert on said entry or topic, it’s not designed to be. It is just a good overview. No secondary source is going to be completely accurate, or engage in the level of detail and nuance which we want from students, or that is required to fully “know” about a subject.