Hi,
Basically, it's using the stepper motor as a mains (line) synchronous motor, which "throws away" almost all of the usual benefits of a stepper motor, i.e. (instant) stop/start, variable speed and reversing. If you happen to have a convenient mains supply, a suitable step-down transformer, two capacitors (to put in reverse-series as above) and want a motor that rotates continuously in one direction at the one available speed with modest torque, then you have a solution.
Most of those questions are unanswerable except by "It depends...." (on the motor, capacitor, transformer voltage, etc, etc.). Synchronous and stepper motors are not really "comparable" with dc motors; when you increase the load on a dc motor it slows down and draws more current, a synchronous/stepper will just stop or judder.
It
might "work" (or at least rotate) with a square wave, but the capacitor can't give anything close to phase-shifting the square waveform by 90 degrees, as it can with a sine wave, so the performnance will be (very) poor. But why bother when you may be able to drive it from a "real" H-bridge with a
20 pence module and two PICaxe pins (or perhaps a 556). Wow, already 8 pages back, but I
will give an update in due course.
Cheers, Alan.