Earlier quoted context omitted.
I actually really like Safari books online, the all-you-can-eat subscription style matches my usage perfectly. My experience has been that most technical books aren't worth reading cover to cover, but many make for great references. When researching certain technical topics, I just open dozens of books and skip straight to the relevant sections.
But even if you like the subscription model, you are forced to consume the content a certain way. If I wanted to read on my Android tablet, presumably I'd use the Safari app ... which barely has a mediocre rating. https://play.google.com/store/apps/details?id=com.safariflow...
My favorite approach is when the author makes the book available online, but still sells the PDF and physical book. An example of this is Exploring ES6 [0]. As a user, it has tons of benefits.
Before Amazon dominated the book space, it used to be that you could go to a book store and browser through a book before you bought it. That way you could do a quick check to confirm it has what you're looking for. But with paywalled digital books you can't do that. For technical books this can be very frustrating, since you might be looking for something more advanced, while the book barely touches on the subject. Having the book available online means you can browse first.
Heck, I wouldn't even mind paying first, if online companies had better return policies. If I get a book and a few minutes in I realize it wasn't what I was looking for, I want to be able to get a refund without having to send 20 back-and-forth emails with customer support. In some cases I just pirate the book, and after giving it a browse, I'll decide to either buy or trash it. Whenever a book is good or helpful, I'm happy to pay because I understand people need to survive. On top of that, it's also in my best interest as a reader that the author continue producing amazing content.
Last perk of having the book freely available online is you can access it anywhere without having to install or login to anything. If you lose your copy, or you're at work you wanna check something... It's really easy to pull up the browser. In addition to that, you can also link coworkers to references in the book, which might get them to buy the book as well.