Look at my post here
https://www.mobileread.com/forums/sho...32&postcount=5
It explains why some people prefer left justification on an e-book reader.
Fully justified text looks better if you just look at the page. But when it isn't done right it can be less [conveniently] legible than left justified text.
This is why I consider user configurability such an important issue. We all all different and if you ask 3 people about what is an ideal book layout you get 5 different answers.