For those that learned Celigo from scratch, is taking Celigo university productive?

Yes it is useful to get started and learn the basics. Takes 2-3h per level, so can complete whole thing in 1-2 weeks. If you already know topics like REST, SOAP, Handlebars, JS - it is not hard. Otherwise it is good idea to brush up on these topics as you encounter them during training. After training, Celigo Documentation is really good for more advanced topics.

I agree, yes, it's useful, especially if you learned from scratch (specific to your business needs) because there's a lot more out there that it can do. I took it after using Celigo for over a year and feel I got benefit out of it.

I would say it is

Reading the docs is always a good idea.