What's really nice about tiny e-readers is that you can read without having to move your eyes horizontally.
If there are only four words per line, you can slide your eyes down the middle and take in all the words in a chunk like you would for normal speed-reading.
I have an xteink X4 and X3 and I swear I can read for much longer without strain. You can also just crank your margins way up on most other e-readers.