I really got a lot out of the Level 1 and 2 certification from SCAA when I did them, but there's still a vast amount that I feel I don't know. I've learned as much, if not more, from engaging with the Barista Hustle community.
Online courses have a great potential for busy baristas too, you can fit it in whenever suits. My SCAA course meant time off work + travel and accommodation costs. Definitely worth it, but not an option for everyone.