The Arms and Equipment Guide should be an important setting book for Dungeons and Dragons - it describes most of the items from the equipment section of the Player's Handbook, often with historical context and illustrations. This is an immense help in visualizing your character and their possessions. It could also aid in getting a sense for what a medieval-esque fantasy world is like, and perhaps even allow players to develop an intuitive sense for the medieval technology level and the medieval way of doing things.
There was a moment like that, when the book stopped to explain the purpose of horseshoes. It said that sometimes a pebble would get between the horse's shoe and its hoof, and that if you wanted to take care of your horse you would have to periodically check and remove any you found. This didn't come as a surprise to me or anything, but it wasn't something I would have thought about. For a brief moment, the reality of owning a horse became a bit more real to me.
But it was just a moment. Most of that chapter dealt with the subject of barding in exhaustive detail. Do I need to know the difference between poitrels and flanchards? Are those even really words? Is this going to have any bearing on play whatsoever?
This is the sort of book that is, technically, obsolete in our modern day. I can search for any random weapon in here and most likely find a youtube video of someone testing it out (I tried this with the halberd and it went exactly as I predicted). There are so many educational resources available to us that make a simple list of medieval equipment kind of pointless. But it does have a niche. The very abundance of sources makes it hard to find information that is accurate, relevant, and accessible to the layman. Collating and paraphrasing a wide range of information into a single reference is pretty valuable.
Unfortunately, the book's accuracy is all over the place. I'm sure we all know by now that studded leather armor didn't exist. Armed with that bit of knowledge, there's a lot in this book that's pretty dubious (for example - the terms "longsword" and "bastard sword" were more or less used interchangeably until quite recently).
Also, its relevance could be hit-or-miss. To wit: Why are there so many fucking polearms? Far be it from me to criticize someone for being too obsessed with the minutiae of their hobby, but Dungeons and Dragons' attempt to convert all of us into polearm enthusiasts is deeply misguided. For crying out loud, the book's whole paradigm for understanding the weapon is flawed. In the real world, the polearm is like a snowflake. A lot of them were different for the sake of being different. You've got 18 different types here, and that's either far too many names for 3-4 different design tendencies or far too few for the literally hundreds of variations that are historically extent. Either way, AD&D's combat system is not detailed enough to actually care about them. A metal bit at the end of a stick. That's a polearm.
And that's the biggest flaw of this book. That it pancakes history into one sort of homogeneous, unrecognizable mass, substituting detail for genuine understanding. The main take away from the polearm explosion should have been that there were a lot of people, over a long period of time, and a wide region of space, doing things very differently. Maybe some of that diversity could have made it into the various D&D worlds.
I mean, for fuck's sake, they listed the medieval fashion terms alphabetically. How is that supposed to help anyone understand how medieval people actually dressed?
The weirdest thing about this book, though, was the little "in-character" narratives that accompanied the weapon descriptions. I put "in-character" in scare quotes because at least half of them directly reference the game's mechanics ("it makes sense to fire darts at their maximum rate.") It was so jarring that the stories had more or less the opposite of their intended effect, taking me out of the fantasy mindset and reminding me that I was reading a reference book.
You can't use the Arms and Equipment Guide to help you build a good fantasy setting, but you can use it to help you easily build a bad one. And that is a much more practical use. To be honest, meaningful storytelling experiences where you use the medium of rpgs to connect to real history are probably going to be pretty rare, even if that's what you're aiming for. A more realistic approach to setting is as a backdrop for improbably fantasy adventures. And for that, the Arms and Equipment Guide is good enough.
UKSS Contribution: There are a few pure fantasy conceits here (elven chain and the like), but one especially caught my eye - Coin Armor.
It's like scale armor, but instead of scales of overlapping metal, it's coins. There's no way in hell that could possibly be practical or effective, but I imagine it looks . . . spectacular.
I am imagining some sort of flamboyant, over-the-top warlord who has enough followers that they don't need to fight on the front lines, but who deliberately projects an image of crass wealth and profligate spending. The coin armor is their signature outfit, something so garish and wasteful that no one else would dare imitate it.