It's a very nice unit. Not sure if Jack had one to play with over the sumemr, but I did. I also have a small cab Leslie with the "cheese wheel" styrofoam drum, so I tend to have slightly higher standards of what a Les compared to folks whose only first hand experience is using phasers and flangers to fake it. This thing nails it beautifully, especially the grind you get when the doppler effect is mapped onto the very end of the signal chain (after the amp, transformer and speaker clipping).
Sadly, the soundclips at the website don't demonstrate the thing in stereo very well. While it sounds great in mono, it sounds fantastic in stereo. You get the real sense of a spinning sound source, not just the notches, pitch distortion, etc. Again, I A/B'd it with my own Leslie, and the mojo is there people, it's there.