This is a really thought-through 5e extension with a good balance of crunch and fluff. The "crunch" presents a system to categorize levels of item customization and enhancement that adds significant depth to a DM and party inclined to go into tricking out equipment. The fluff provides specific examples of that customization that both DMs and players can not only use right away, but also use as inspiration and gauge for their own homebrew.
I specifically intend to use this system to augment or replace the now-official 5e artificer "infusions." I cannot overstate how important it is that there is a system here, as the 5e solution strikes me as arbitrary and half-baked. Wizards really should have licensed this off Ms. Gregersen and ended up with a superior implementation. Too bad for them, but don't miss out -- buy this and give your artificers some real power!
[5 of 5 Stars!]