I've had a few Kindle devices and I read almost exclusively with the Kindle app on my phone/iPad. I bought one of the first Kindle devices, and have likely read close to 1,000 books across a decade+. A few thoughts:
- App - The app is nice in that it's always with me. I can steal 5 minutes waiting for food, an appt, etc. It works at night/am, and I can read in bed easily for a few minutes. I usually use a black background, white-ish text, and I can grow/shrink text easily, depending on whether I have classes or not. Downside is the brightness at times. Especially at night. I turn it way down, but it still is bright and fatiguing at times.
- Kindle device - it's like paper most of the time, and you can easily see text. Grow/shrink, etc. you can carry lots of books on there, and battery lasts a long time. turning pages is with the buttons, and you can "select" images and grow/shrink or scroll around. The newer devices have some backlighting if you need it, but less fatiguing on eyes. I've seen people drop them in a ziploc for beach/bath/etc environments. Way easier to read outside than the app/phone.
Honestly, for tech stuff, they both such a bit. I read some business/nonfiction and getting a chart/image and trying to zoom in is hard. Often I can gloss over those, and then pick up some details on the computer, where you can use the "Cloud Reader" in a browser and get a better view. This happens when I send PDFs over, and so for code/image/tables, I will go back on a big screen to really see what the info is. The plus side, too, is that I can copy/paste stuff over from the cloud reader to SSMS/VS/etc.
To me, they are really if you want to consume text. I get a lot of books from the library as well as AMZN. I can email PDFs in and read them, but it's about convenience and seeing text. I find images/code/etc are less useful on the e-reader. Of course, they are a PIA in paper as well. Trying to keep a book held open and type in code stinks.
The Kindle devices are nice. I might suggest you try the app first, and see how your eyes adjust. My wife thought it was stupid in 2010, but tried it for a couple months and she uses it constantly now. The kids liked the devices more, because they were closer to paper. They are small and easy to carry around, and fairly cheap, but try e-reading first, then decide if you want to get a specific device.
I do like e-ink, but I don't want to carry another device and my phone works well with the 5" screen.