I'm happy to read on a small device as long as the font and screen are good. I started out ereading on a Casseiopia EM500, and moved to reading on my original iphone (3.5"screen) which I then continued on my 3GS/4S/5S. IN the interim I bought a Sony PRS-650 because it seemed like a good idea at the time. Still have it, battery is still good, hardly ever look at it except to charge it up. Ditto a Kobo Glo then Kobo GloHD. And, I am still reading on my 5S, in Stanza (3.5"), which has yet to be surpassed in terms of how I like to read. In bed, laying on my side, late at night before sleeping, one hand in use.
As always its horses for courses