I can't take a pciture right now but here's an old one comparing Japanese manga with 6" reader.
https://www.mobileread.com/forums/at...9&d=1323364822
H2O with 6.8" is "just right" for this format.
Of course, a bigger screen never hurts. And when Japanese manga get translated/printed in the US they're probably a bigger size than the Japanese format

so "big enough for manga" depends a lot what you're used to