As far as I can tell, they're only good for one thing: reading comics, or articles. (although the form factor should be good for books, they generally fail for non-tablet related reasons: most ebooks contain DRM, and so you don't own them. This is less of a problem for articles or comics)

They're bad for everything else:

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- Typing anything whatsoever

- Clicking links. (my thumb is not large, but is still much bigger than the target text I need to click much of the time)

- Being easy to hold: most of them are very smooth and slick, which means you can't prop them against anything, and have to constantly be holding them. Typing, while holding them is very uncomfortable, and all around worse than typing on a keyboard.

- Having physical buttons.

- Having a good and consistent UI. (I dislike having new gestures to learn and use every few versions)

- Staying upright while you try to watch video

- Not invading your privacy every moment of every day

- Receiving security updates after one year of ownership (or, if you own an Apple device, this can be swapped out for "being inexpensive or open")

- Loading the desktop version of sites

Generally speaking, they're worse at everything compared to a laptop, and are only slightly more portable.