I'm blanking on the name, but there was an older 5-way switch keyboard, where the 4 non-thumb fingers went in a recess with 4 paddles and a push-button; I've known several people who used that because of severe RSI, but it was quite expensive.
Yes, this is actually what lead me to the CharaChorder! The data hand seems superior for single letter entry, but the CharaChorder has a type of chording built in to the firmware. I imagine sticking their chording engine in the DataHand would be incredible.
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Searching split keyboards on google image search for long enough found it: https://en.wikipedia.org/wiki/DataHand#/media/File:DataHand_...