Udemy has the potential to add a lot of income to those who publish Non Fiction Books.
If you have a book on Amazon and other platforms that is permafree you can drive traffic to a Udemy course of your own (that you can create easily if you have video creation skills of can hire someone to do that) and upsell your readers to a higher priced product.
An example of how this would work...
Let's say you have a fitness book that is available free on Amazon and elsewhere.
That book could give readers a lot of good quality information and also encourage them people to check out your Udemy course to get video training on what they have learnt in your book.
You could have a free book on weight loss or weight gain and in the book upsell them to a video course to give them a higher level of training.
This could be highly effective for people with books on business of any kind, entrepreneurship, real estate selling, any selling etc etc.
There is a lot of potential if you think of how it can be used with your info business.
And as a side note, if you came to learn about Kindling through Internet Marketing then you could upload your current or past training product in Udemy to target a whole new market.
Here's the link for the training... $2k on Udemy in under 2 Months
If it's relevant for your current business model then I can say, I've checked it, it's good and it is a fast way to learn what you need to do.