I'm not sure if you wanted feedback from users or the builder (me). Here's my .02c worth.
The idea behind the Single Stage is that there is no other reason to reduce motor rpm to 100 at the chainwheel and then overdrive it back up to 400 at the rear wheel other than to match motor rpm to rider pedaling cadence. RPM matching is okay at lower power levels, but when you get above 2000 watts the torque multiplication meeting the resistance of overdrive gearing tears up the driveline. Plus if you match motor rpm to pedaling rpm and then run it through the normal bicycle gearing, top speed is limited to how fast you can pedal. The Single Stage doesn't try to match motor rpm to pedaling cadence. It optimizes the gearing for the motor. The chainwheel spins at 500 rpm and even with 1:1 gearing (22t front and rear) top speed is greater than with a 100 rpm chainwheel drive. 1:1 gearing has much lower resistance than 1:4 overdrive. Try it on your own bike, if your low gear is even 1:1. It's easier to pedal in a lower gear. When you try to pedal with 1:4 you can feel the entire bike straining under the load.
Here is a comparison chart of the speeds in each gear in a single stage drive with 6:1 motor reduction and a two stage drive with 30:1.
By making more speed in a lower gear the Single Stage sees reduced driveline stress and higher power capacity. One of my Single Stage customers is running 100 amps through his 8 speed bicycle driveline. If you try that with 30:1 reduction and a 100 rpm chainwheel speed it would immediately destroy some part of the driveline. Too much torque meeting too much resistance.
Here are a couple of beauty shots of the Single Stage and a shot of the bike that's running 100 amps through an 8 speed.
Here is a video of the bike above running through the gears.
https://www.youtube.com/watch?v=nZHnSWWN9NY
[youtube]nZHnSWWN9NY[/youtube]
The downside of the Single Stage is that you can't pedal with the motor (unless you can pedal at 500 rpm). The upside is reduced driveline stress, higher power capacity, and higher top speed. You can pedal through the Single Stage if the battery dies. The 11t rear sprocket will give you 1:2 overdrive which is good for 15 mph or so. It's a good "limp home" mode if you suck the battery dry.
For people who like to pedal, I have a couple of different two stage drives that match motor speed to pedaling cadence. I recommend a maximum of 2000 watts through that much reduction. In the very near future I'll have a Left Hand Drive (LHD) that will run one speed for the motor on the left side and leave the bicycle driveline stock on the right. That drive is like having a powerful hub motor, only with good weight distribution, low unsprung weight on the rear wheel, and reduction gearing.
[moderator edit to fix youtube link]