Looking for nucl.ai courses opinions

Hi! I want to be very good in AI ( I really like it) and I'm looking for courses to improve. I've been looking at the courses that nucl.ai. It seems to be good, but I want some user input. Anyone here knows anything about it?
Is it worth to pay? I can see that most of the videos are free (except unit 2) and I don't really understand what are you paying for.
Thanks people!