Personally I wouldn't use any such site even for Public Domain.
Calibre is "free" (please donate) and has been trouble free for me on XP, Win7 and Linux.
Runs on MacOS, Linux and Windows.
It's far better and more flexible than any online site.
It also is the best way to manage more than 50 books, one device, several and works with Kindle, all makes & models of ePub based readers I've tried, two Android phones and two Android tablets I have, all different versions of Android.
It also does a better conversion from docx to epub2 and upload to Amazon for Kindle, than uploading doc or docx or mobi direct to Amazon.
Also this site hosts Kovid's excellent support for Calibre.
https://www.mobileread.com/forums/fo...play.php?f=166
He's courteous, helpful and unlike Microsoft, Google or Apple, he actually listens and fixes stuff!