3rd Party Study Guides

You guys have probably heard this question a million times but I wanted to put it out there again. How effective are 3rd party study guides for helping you pass? Why do they work when the real material and everything thats going to be on the exam is explained in detail in the CFAI books? I passed level 1 without any 3rd party study guides, would level 2 be any different if I’m putting in the hours? I feel everyone has either bought into 3rd party material or hasn’t. Anyone in here experience both sides (with and without additional material) and have any comments?