I just got my Boss RT-20 Rotary Pedal and I have to say it does a very convincing leslie sound. I have not tried the other "boutique" options such as the Option 5, Korg G4, etc. but I am extremely pleased with the tone I am currently getting. On "Slow" mode it sounds very chewy and the particular tone I was looking for was Joe's take on "Tea for One". Nails it. The "Fast" setting ramps the sound up and nails the "Cold Shot" sound. 2 sounds at your feet that you toggle between all in one pedal, pretty cool. The added "univibe" setting does a decent job for that kinda sound and the fact that it is cheaper and more readily available than many of the boutique offerings is icing on the cake. Recommend it in the FX loop.
'67 and '74 Fender Twin Reverbs, '74 Marshall 1987 lead mkII, Metro Superlead 100. Pedals from TC Electronic, Ibanez, Dunlop, BK Butler, Electro-Harmonix, Fulltone, Maestro/Gibson, Loopmaster switching, VoodooLab, Boss. Gibson and Fender guitars, Dimarzio pickups.