you are ruining your eyesight by using such small display/letters and fixed focused distance, it may not look like that when you are young, but give it few year

you are ruining your eyesight by using such small display/letters and fixed focused distance, it may not look like that when you are young, but give it few years and you will see results 4.2" is OK for temporary reading for very short periods, but ebooks are usually used for long reading sessions and one would want to use it for years before throwing away