Introduction to Objectivist Epistemology is what it says on the tin: an introduction. The original book was extremely short, barely 100 pages. An additional essay by Leonard Peikoff and extensive discussion transcripts are included in the second edition. The transcripts come from a series of workshops conducted between 1969 and 1971, discussing Objectivist epistemology with about a dozen (anonymous) professors.
I would advise against reading the appendices on a first pass through the book. It’s not that they’re bad, but they contain a lot of high-level material that takes a long time to process usefully. Fully comprehending the basic concepts put forth in the main text is higher priority. The appendices are included to help flesh out the information academically. Lay readers can probably skip them entirely.
The basic concept which Rand is trying to get across is measurement omission. By this, she means the process of noticing similarities between the essential aspect of concretes, and thus developing general categories that omit the non-essential characteristics of the concretes. This, Rand argues, is the crux of concept-formation.
Objectivist concept theory is very similar to the reductionist model. Unfortunately, I don’t think Rand spends enough time explicitly arguing against the idea of things having essences. A lot of Objectivists still get hung up on “but it is a X?” questions rather than one would naively expect. This is a metaphysical matter, but a relevant one. Rand is very clear in all her works that epistemology follows from metaphysics. Getting epistemology right is a lot easier you’re your metaphysics is right, though developing an accurate metaphysics requires a functional epistemology.
Spending more time on philosophical development would have been valuable. Instead, the details of concept formation—what concepts are valid, what concepts aren’t, how to tell the difference, and so on—are the bulk of the book. This is, possibly, more practical, and Objectivism is a philosophy for living on Earth.
Still, I’m not sure that practical philosophy can achieve wider acceptance without stating the case clearly, in language that serious lay readers can understand. The appendices cover a lot of important ground, but not in the most efficient manner. Writing summaries probably would have been more efficient, but ARI Objectivists tend to tread carefully when it comes to interpreting what Ayn Rand really meant. Naturally, they opted for edited transcripts over new material. This gives a better insight into the ensuing philosophical development, but makes untangling final conclusions slow and laborious work.
Nevertheless, I would recommend Introduction to Objectivism Epistemology. It covers a number of useful ideas for developing a personal theory of knowledge, and warns against several common pitfalls. The main body of the text is interesting and readable, but the appendices are a bit more challenging. Non-academics should probably just skim for material that looks interesting and avoid reading those sections in their entirety.