The PX4D unit has two rotary effects: on the first you can set the Leslie speed to anything you like, I prefer slightly slower than the top speed. If you change the speed mid song the effect realistically ramps up or down to the new speed. The second effect is velocity sensitive - play quietly and the speed is slow, pick more heavily and the Leslie ramps up. As you can imagine, a bit of practice on the volume pedal and you have a very expressive effect.

The PODxt also has two rotary effects and both are somewhat more convincingly B3 sounding than the Korg. You have the benefit of tone and mix parameters, however the Leslie is either 'slow' or 'fast' (ramping automatically between the two).

With some tweaking (especially with the cabinet/amp modelling) you could probably get the Korg to sound a bit more authentic. What it may lack in sound it more than makes up for in sheer noodling around fun. It's great to be able to get Leslie speed changes without having to ride a switch with your 'spare' hand. You can get a decent enough straight steel sound with delay/reverb etc, also there are some other things in it's favour apart from the price and size/weight such as built in drum machine and phrase trainer.