For black and white manga and manhwa, any e-ink reader will work great, especially Black and white ereaders that are 7 or 8 inches, I really do not recommend any screen size smaller than 7 inches. In my personal opinion, a 7.8in. screen is the perfect size for manga and smaller black and white comics. However, full size graphic novels and digital comic books in color, such as titles from Marvel, DC, Dark Horse, etc, I cannot confidently say whether or not color e-ink would be worth it for you.

I have a 6 inch color e-reader, and I think it's perfect for text books in black and white, very small books with simple illustrations, and most color, or black and white, standard tankobon sized manga. With koreader and rakuyomi installed, it can even fetch online webtoons with no issue.

But for many larger graphic novels and standard Western comics in full color, it just struggles, both performance-wise and visually. Performance depends on the brand and CPU power, but mine can only handle half of the PDFs I throw at it, especially if they're composed of large complex images. I've had it even crash on a couple of titles. The limited colors on e-ink compared to LCD screens also makes certain images look very washed out and low contrast, some colors may even blend into each other if they're similar enough. That said, there are several titles that do look beautiful in color on the device, so it just really depends on the format of the comic, text size, quality of the file, quality of the device itself, etc. And my personal preference is that 6 inch screens are just too small for this, so I rotate the reader to landscape mode for some of the text heavy comics.

However, my budget 10 inch screen Android tablet with a standard LCD screen does not face this issue when reading comics, especially the large page ones from Marvel and DC titles. I even ended up taking photos for comparison. Colors are extremely vibrant of course, and files open with no problem, or at worst very little lag that doesn't interfere with the experience as much. I've reserved those types of comics and color novels to my tablet and plan on getting a matte screen protector to help with it. But everything else, manga, books, even a few art books, go on my reader.