Keyers are keyboard-like devices (without the board) which enable the user to type with one hand using a chording layout.
(pictures from wikipedia)
I can see the theoretical advantage of such a device, if properly designed and built.
Stenotype, which you may or may not know, is by far the fastest widespread input method for text. Alas, it uses a phonetic system which is hard to learn and even harder to implement without very expensive special tools. It does however show the potential of chording as a fast input method.
Commercial keyers in existence are going about this by making a lot of keys available to each finger. I think one key/switch per finger is exactly the right amount. Just squeezing given combinations of keys, without having to move the finger forward or sideways, would likely be very fast.
Five switches produce exactly 120 different combinations (5!=120). That's a lot of characters (119, because zero keys is a combination which we must account for). But some people (coders) would probably need more, so I wouldn't mind having an extra switch on the thumb, just for accessing "extra" sets. Mind you, 6!=720.
Perhaps some setting in the OS would determine the time interval to consider a switch to be or not part of a chord (think double click interval in mouse settings). Really fast "keyists" would have this reduced to <10ms.
The layout would have to be figured out to favor the most used characters, but I really think that any combination would be pretty easy to actuate. I hereby offer the suggestion for the 5 keys press (AKA, the RAGE squeeze). It turns the keyer off. And on. Yes, it's wireless. So, there you go internet, you only have to figure out the other 118 (or 718).
I love the idea of sitting in my couch, grabbing a yet-to-be-invented ergonomic keyer in one hand, a single malt on the other, and comfortably type away at breakneck speeds. But for most people the potential would be in wearables. Google glassing it on the train home.
So, what do you guys think?
