The RotoSIM is a mind-blowingly great Leslie speaker sim with two speeds and separate levels for the bass and tweeter. Output A is designed to sound slightly different than Output B. Output A is a little more transparent and truer sounding.
Output B is deeper and thicker sounding. Definitely experiment with both outputs while the instrument is plugged into IN A (this also gives a nicer stereo sound spread when used in stereo).
It doesn't get much closer to the real thing!
This is a used RotoSIM shows signs of love and use but still sounds and works great! It ships the next day!