This piece is fantastic.
It takes the incredibly stripped down armour system in 5th edition, pulls it out and polishes it to a shine.
The worry with supplemental systems for things like armour is that you'll end up with something unwieldy or overly complex. The Armorer's Handbook feels like it could have been slipped right into the Player's Handbook and the only reason people would notice a difference is because it's better organised.
As someone who dips their toe in game design it delights me to see how much work went into refining and polishing this. A must buy.
[5 of 5 Stars!]