Well I won't knock somebody for making an informed choice. If it fits your reading style, all the power to ya.
My uneducated choice is to stick with epub, because I know it's universally supported, and my next device won't likely be Kobo thanks to them ditching the SD card slot. Actually there's plenty of reasons to ditch Kobo, but having all my books on one device is the clincher.
Despite these petty first-world gripes, I'm very happy Kobo exists.
In Reading Settings in 4.5, "display progress for current chapter" is an option. I don't have any kepubs on the device. The only epub book I've tried this setting with shows the total # of pages in the book as opposed to what's remaining in the chapter.
I'm quite confused how font weight variance is practically applied while reading a kepub? Do they dynamically change throughout the book to help differentiate content, or is it meant to be set manually?
If manually, I've loaded a few of my favorite fonts at varying weights, and can choose the weight preferred while reading epubs. My only regret was loading Amazon's Ember and Bookerly. What a waste of bits!