[gtrevorjay]

One-handed daily drivers are out there. We're nuts, but at least it's not Dvorak (kidding).

TBH, the the Twiddler layout is probably superior (though not by much). I went with eight traditional keys because it could be hand wired. The Twiddler approach is basically limited to soldering directly to a board, with all the issues therein. After about six months or so I would get debris caught under one switch or another and the Twiddler is basically welded shut. :/

Speaking of design issues (and talking about the BT). I highly recommend using a Nice! or other wireless/BT microcontroller. Not only is it more convenient but cable strain is a real issue on most microcontrollers. If the Handler has a design flaw, that's the biggie.