Very easy, if you are the “all my metadata must be perfect” type person then it plays well with Calibre, if you are a just “put it on I don’t care” , all you need is a web browser and WiFi connection or something that recognizes a flash drive including tablets/phones.
The point about DRM is more that for stores like Amazon, you can only remove the DRM anymore if it’s on a physical Kindle connected to Calibre with the right plugin. That doesn’t work on multipurpose tablets like the boox.
Koreader works great on kobo, installing is a minor effort.