I wondered how the creator of this course could guarantee the course would be available forever, and what a headache it must be to continue to maintain the hosting/content if sales taper off. Outsourcing that job to a service which is hosting many such courses (and with new ones continually added) makes a lot more sense here, and of course you have bills to pay too. That 20% commission isn't just covering the cost of time you put into the course builder and hosting now, it covers hosting in perpetuity.
As a comparison, Leanpub charges 20% for books/courses (not sure if those courses are on par with the features offered by tigyog). You'd get better pricing with Gumroad, but no interactive features on that platform. 20% is more than fair in my opinion.
Side note on nav UX. I expect a right click on logo to be able to open up the tigyog landing page, not save image dialog.