mechanic courses

Which is the most useful cycle mechanic course out there (Cytech C&G, private org)?

I’m more than confident at most things, I have built bikes, maintained bikes and built wheels, etc. I’m aware that a weakness is knowing the things that I don’t know. I wasn’t aware of freehubs with enclosed sealed bearings that can’t easily be removed from the hub, but have stripped and rebuild the freehub on Zondas.

Diolch/gracias/thanks.