I found the core Lazy GM book worth reading, although if you listen to his podcast or watch him on YouTube, you probably know what it's going to say. The workbooks, etc., look good but I never used them and ended up selling them to someone I hope will get more use out of them.
Forge of Foes, though, I have been using to make custom monsters and my players can 100% tell when I'm not using a stock WotC monster. No one has complained yet, but the book definitely makes players sweat more than the Monster Manual does.