[rakoo]

Save as ebook extension (https://addons.mozilla.org/en-US/firefox/addon/saveasebook/), everything goes in a folder managed by syncthing so I have it on my smartphone as well.

On the scale of years, products fail, get bought, are unmaintained, become too expensive, etc... An export of your database is always a hassle to manage, and you must hope there will be an importer for the next product that will also fail a few years down the road.

On the other hand, files have always been there and will always be there. Epub is a standard-enough format that will live. The highest piece of complexity is syncthing, which can be easily replaced the day it doesn't work anymore. Bonus: I have all my data offline so I don't need connectivity, and I lower my environmental impact.

Too often products feel like a reinvention of the whole stack because it's easier to sell, rather than reusing proven tools and using them the way they were supposed to be used.