I've got an older version of one of these...
I've always liked the idea of the Microwriter and bought a Twiddler many years ago. It was not multi-platform and so I abandoned it. Dog knows where it is now.
I'd buy one of these to help me with my accounts, where I need to type details from stacks of receipts into a spreadsheet. At the moment I use voice recognition software but that's not 100% reliable (e.g. "for pound 50" instead of "£4.50").
A Twiddler would let me pick up each receipt to read it and type in the details at the same time.
Why does it have to be so for king expensive? Probably because it's a niche market. :-(