I have not the wide technical insight of most regular users around here but I will provide you with my experience. When I got my Clara in May I had the same question as you and I came across multiple answers pointing towards KoboTouchExtended, as others have mentioned. It's a plugin for Calibre, you simply install it (Under "Preferences"->"Plugins"->"Get new plugins" and search for kobotouchextended) and Calibre automatically sends your epubs as kepubs to your Kobo devices. You don't have to worry about anything, your books in Calibre are still the same epubs, they are simply transfered as kepubs to your Kobo. You can check if your books have been correctly sent as kepubs if you see "Kobo epub" on the "my books" menu instead of simply "epub". As for the pros of using kepubs, I don't think there are many, but my reading experience has been great with kepubs so far. On a 6 inch screen it comes handy being able to zoom some pictures and I find myself regularly using the feature to see the book stats with the chapter's remaining time and the chapters' lenght comparison as a bar graph. It is a nice visual aid with useful information absent for epubs but it works great with my sideloaded books.