I've only offered one "beta" course on the Teachable platform so my review is from a beginner. I found it reasonably (not entirely) easy to use, it seemed to "do the job" and the support team was helpful.
The setup of "school" versus "course" was a little lengthy and confusing. I also stumbled with the timed release of lessons which weren't supposed to go live until a certain date. And parts of the interface, including previewing my course, were clunky. My main hesitation is in value for money: the commission fees on the basic plan are steep (I think, actually, I was overcharged and later refunded with no explanation) and I'm irritated there isn't better reporting available at this basic level... which, by the way, still isn't cheap! I'll be looking at other options as I get ready for my next course.
Someone who has enough students / courses / revenue to justify one of the higher paid plans. Not great for those just getting started with online courses, as there is a learning curve in getting started and the fees for low-volume players are steep.