Hunter S. Thompson had this great quote at the beginning of Fear and Loathing in Las Vegas: “…once you get locked into a serious drug collection, the tendency is to push it as far as you can.“
This reminded me of that quote, just with ttrpg rulebooks. There is absolutely no proper reason why I am having two of those. I had the one with the color cover before (version 1.4 from what I can see), but a recent trip to Amazon made me buy the black and white version as well (version 2 I think).
And I really haven’t found a reason to even play this yet, although the books are short and cheap enough for some ideas: they are full games based on the original white box rules (via Swords and Wizardry as a retroclone of that), they are a handy size (A5?), and they are cheap. I don’t remember what the left one cost, but I bought the right one for under 7 Euros. Technically, if you wanted a quick game with simple rules, you could just go on Amazon, buy a few copies of the book for all the players, print a few character sheets, and be done with it. Maybe throw in some cheap dice for everybody and you have yourself a game and all your players now have rulebooks and gear for less than the price of a single 5e book.
The rules are your standard Swords and Wizardry clone, just scaled back to emulate the White Box era of rules. They of course are subtly different from all the other OSR rules or the original, but they still work out well. The b/w version has better art and layout, but personally I love how dorky the left one looks.
It does have the single saving throw mechanism which I dislike, but I can live with that. That’s a bit of a pet peeve of mine. In my personal houserules I replaced the usual B/X rolls with the three-tiered system they came up with in third edition, but somehow reducing it to a single roll feels wrong.
I find it interesting that people like to recreate the roleplaying aspects of things, but somehow leave out all those wargaming aspects the rules were originally written for. The original rules were intended as campaign rules for wargames (specifically Chainmail), but most of that content has been stripped out, not only here, but in most retroclones.