But again it's proven how *much* more popular smartphones are than tablets (sigh); after the 5.5-inch smartphone became popular (like the Samsung Note and iPhone 6+) it seems this market has really flowered: a quick search for Portable Keyboards yielded lots of results, and even better: they generelly have good reviews and very reasonable prices (less than half of what they cost a couple of years ago). And there are many shapes to choose between.
I've ordered one (EC, wireless for iOS, Android and Win) which when folded is admittedly thicker, but barely larger than the big iPhone! A big-phone screen is eminently usable for writing, even serious writing, and if the keyboard works as well as a classic one I have of similar size (the old Think Outside), it is very usable even for touch-typing (folded out it's close to Full Size). So with large pockets, look out, the writer is in town.
UPDATE: sadly it turns out that the keyboard below is a bit heavy in real life, and also it has that unfortunate/idiotic design where they have put an arrow key where you're used to hit the shift key...
|(This is even the smaller iPhone.)|
And of course what with modern smartphones having excellent still- and video cameras, it's a journalist-studio-in-a-pocket. Hell, it even includes the publishing- or broadcast studio!
I've had a love affair with writing in cafes since reading an article about it in 1992, years before I ever got a laptop!