Weakest part of the instrument, IMO. Not a bad Leslie sim, if you tweak it a bit, but it suffers from having very few 'straight' organ tones. Pretty much all the organ sounds got SOME kind of Leslie or chorus sampled into it. Some got pretty good F/S settings, even. But ramping up and down is important to me. It's like the way a singer starts to add vibrato to their voice - very individual and expressive. So only those few 'straight' tones work with the Leslie MFX sim, otherwise you put the sampled Leslie through a sim, it comes out all nasty and phasey...

But that's just me being ultra picky. Compared to some budget arrangers I've heard, you MIGHT find the GW-8's to be fairly decent...

If you search for GW-8 here, there were several fairly detailed reviews a while back.