On the recommendations of some folks on the forum, I bought this, and I have to say I’m very disappointed. I bought the complete set, and I’ll stop short of saying I was “scammed”, but I’m very disappointed with it. The way it is marketed, volumes 1-4, it leads the prospective buyer to think it is a series, like an encyclopedia, with each volume covering different topics. This is not the case, and I just spent $200 for 4 versions of the same book. Volume 4 is nothing more than an updated version of volume 1, and the table of contents and subject matter is identical for all 4 books. So, for anyone else thinking about buying one, don’t make the mistake I did. Volume 4 is all you need. They REALLY should make them label it 1st edition, 2nd edition and so forth. To buy the whole set is akin to buying Rand-McNally Road Atlases from 2019-2023. The 2023 is all you need.