I never had performance issues, but I don’t read huge books or anything. There seem to be some online converters, but I agree that is not the most ergonomic. Maybe calibre-web could also do the job, with you connecting to it through your phone’s browser.
Never heard about the kepub
format but I’ll look into it, sounds cool.
I think they meant the HTC entry in the article, not literally the HTC One phone.