I used to own one and have probably written about it before; the side to side is not very natural, but no big problem because the fingertip is down in a well with buttons wrapped close around it, so it’s a small movement, and the way the key mechanism works is backwards to normal - instead of pushing all the way until a contact clicks, the keys are magnetically latched at rest and you push them away from that state, meaning it registers at the start of moving not the end so again small movements and you don’t push hard into a resistive surface with the side of your finger to make sure it registers, you flick a gently sprung thing. Look at the keyboard layout too, shown at the top[1] and the pinkies don’t have sideways movement for writing English letters, and the other fingers only go one way, the easier way, for letters.
I didn’t get used to it to use it exclusively; it’s too tuned for prose, extracting your hand carefully to use a mouse, not having an easy way to type anything one handed while holding a mouse or phone (e.g. hold a device type the serial number), awkward arrow keys and less convenient numbers, see “NAS” (Number And Symbol) mode on the diagram entered by right-thumb-down.
It’s been long enough now that I’d like to play with one again, for a bit of novelty.
[1] https://upload.wikimedia.org/wikipedia/commons/b/b5/DataHand...
