The desire (a.k.a. need) to have a portable means of communication besides pen and paper has been around a long time. This is the ultimate in portable typewriters, “practical” I think only in the sense that it is indeed quite portable. As far as I could tell, you use it by sticking a piece of paper in this thing, rotating the dial to the first letter you want to type and pressing down, then repeat after rotating to each additional letter in turn.
Typing with your thumbs on a phone keypad may seem slow but using this device must have been excruciatingly so. I’d lose my train of thought before I could get a sentence typed out on this thing.