M
Just to be clear, my proposal for a hand brake was not as a substitute for mastering the OneWheel's natural braking mechanism, but instead was just for a type of backup brake for those who are still trying to learn the OneWheel.
Some (like myself) had never had a skateboard before and so there has been a fairly steep learning curve with the OneWheel. In particular, both myself and a couple of my friends have had rides where we got going faster than we are comfortable going and then found it hard to immediately shift our weight to slow down (while maintaining our balance) and had to jump off.
In such circumstances, I think a hand brake would have been a good option, even if only during the first few weeks or months of practice.
I also have seen that some other commercial powered boards have hand brakes by default, so I'm not sure why so many think it's a totally bad idea, even if advanced riders would forgo it (and likewise recommend not relying on it).
That said, thanks for all the tips, which I've been incorporating into my practice schedule. Smart practice does make perfect---