I took a spin on one a few weeks back during SuperPedestrian's regular Friday afternoon test ride sessions. The ride was really short (about 8 city blocks total) and flat, so not a great test. It definitely worked, and was pretty unobtrusive and responsive. I would not call it 'fast', but that doesn't strike me as their goal..
I had a good chat with a representative after my ride; they seem to be focusing a lot of energy on the software that gathers live data from the wheels through the phone and packages it up for presentation to city planners and transport engineers. It's all very noble and such, but it's a lot for a small company to take on. I got the sense that the wheels are pretty much done but getting the ecosystem in place is holding them up. He also mentioned that there are about 300 components that go into building a wheel, and supply chain issues can constrain their manufacturing on short notice.
I'd be happy to try and answer questions if you can think of anything.