Not sure if it will work for fiction books, but I have seen people self publish e-books hidden behind a simple Stripe payment. Should be relatively easy to set up as well.
I believe ddevault published his Wayland book this way.
I believe ddevault published his Wayland book this way.
An important feature I like is the ability to update the books (due to s/w versions, typos, adding new content, etc) and notify the users regarding the new version.
Another feature for both sites is that customer can pay more than the price of the product. And that does happen often enough to make it a highlight of using their site. But this may probably apply more for technical books than fiction.