On E-Readers

Over the years, I have asked quite a few people who have gotten used to e-readers (as opposed to loyalists who stick to physical books), if they prefer horizontally swiping to turn pages, or vertically scrolling to.

The way I see e-readers or reader apps, there are 3 action choices:
Horizontal or vertical scroll
Firstly, just as a preference.

Skipping Pages
For horizontally turning pages on some apps, you can do it by simply clicking on the right side of the screen to move to the next page. Or imagine when you use the arrow buttons on the Adobe Reader to move pages. Sometimes you could rapidly click more than once and it turns more pages than it should. It could also happen with apps that are a bit too sensitive to user input, and you could unintentionally turn more than one page. And if you are not fully there, you might not even realize you’ve missed a page and just keep reading.
That risk isn’t there with most vertical scrolling since there is a sense of continuity, and even if you were to flick your finger and the e-reader scrolls multiple pages, you would see it happen and know you need to move a few pages back. And finally,

Range of Eye-movement needed with horizontal and vertical scrolling
With horizontal swipe, your eyes would need to move from the top to the bottom of the screen, and back to the top, with each page. However with vertical scrolling, the eyes need not constantly traverse the length of the screen but can oscillate in any ~10-100% of the length of the screen depending on how often you choose to scroll as you read.

While horizontal swiping might be the popular choice, I’m not sure yet which one is purely more efficient for reading.