I've used the Android app on both a Nexus 7 and a Galaxy Tab. In both cases, the mechanics are quite different from my physical Kindle (a Kindle 3 with keyboard). I'm not saying if the app is better or worse than the Kindle; the each have their pros and cons.
In general, I prefer the physical Kindle for "relaxed" reading: when I just want to lose myself in a book without worrying about swiping or long presses or navigating menus. But I prefer the tablet app for technical books and some magazines, because it is much better for displaying diagrams, maps, tables, etc.
A few other points:
- Searching is easier on the Android because you use a large touch-screen keyboard for entering your search terms rather than a tiny physical keyboard with minuscule keys. But the actual search itself is faster on the Kindle.
- The Android app displays advertisements (or, rather, "recommendations") at the foot of the home screen, which you can't turn off (as far as I know). In fact, these are not particularly intrusive, and some people might welcome them.
- The Android app has some minor glitches when working with periodicals. The "next article" and "previous article" menu at the bottom of the screen does not show the relevant article names. And if you go out of the app and come back in, it takes you back to the periodical's contents page rather than the last page read. These issues do not apply to the Kindle.
- With the Android app, the Back button doesn't always work. More precisely, it sometimes takes you further back than you want to go. For example, if you follow a link to a footnote, and the click the back button, it takes you all the way back to the home screen rather than to the original page.
- Installing purchased dictionaries is very much easier with the Kindle. It's not much more difficult than buying a book. With the Android app, you have to jump through hoops.
These are just a few points off the top of my head. No doubt others will add some more.
Mike