I'd never heard of Fly Lady and when I looked at the website I could see that many of Babatua's ideas were really straight from there. Fly Lady presents them as plain old common sense (and they are) and is clearly aimed at women, and perhaps particularly at women who are struggling to keep their heads above water. (CHAOS for example stands for Can't Have Anyone Over Syndrome.) It has 500,000 followers.
What Babatua has cleverly done I think, is to make common sense cool, not boring. (The Fly Lady site is decidedly uncool.) He makes it look like a sophisticated modern philosophy (Minimalism), with a touch of eastern allure (Zen). He has also made his site attractive to and relevant for men, and the trendy young. He has 250,000 'crazy, sexy, cool' followers....
Though I don't subscribe to either, preferring to dip in when I want to, I like them both and have found helpful and occasionally inspiring stuff on both sites.