I just bought the VK-8m module.
The sound is as good as you would expect, being I believe identical to the VK-8 keyboard, which definately rivals the Hammond XK-2 and the Korg CX-3 for most authentic organ simulator, with the B4 plugin being the Dark Horse in the race. Each have their forces and weaknesses, so it's a matter of taste. The VK is probably slightly inferior to the others, but is for the moment the only one available as a module. Other modules, such as the Hammond XM-1 or the Oberheim OB3ex are definately way below this unit. The Nord Electro Rack sadly doesn't have any physical drawbars, in spite of a great organ sound.
So the VK-8m is doing good compared to the competition. However, there are a few things to moan about. The various advanced settings are ridicilously difficult to acces. It's a complicated procedure of arbitrarily pressing various buttons, and there is no way to go about this without having the manual next to you. Not a great advantage if you're on tour and need to change a MIDI reveive channel or adjust the speed-up ramp for the leslie.
An even bigger problem is the lack of a leslie speed foot switch input (!). The only pedal input on the VK-8m is for the expression pedal. You could switch the speed with a pedal by hooking up a foot switch to your controller keyboard and program it to send MIDI controller ID 80, but if all you have is a basic master keyboard, or if you're using a rented keyboard on a gig, you might not be able to specify which controller ID the pedals send. Especially since controller 80 is rarely utilised. They should have assigned the leslie speed to the Hold pedal ID (64), which is available on any keyboard, and who's using a sustain pedal on an organ, anyway?
The omission of the pedal switch is mysterious, since Roland chose to include a D-Beam controller. This can be used for various purposes, including Leslie speed (this doesn't help you, if you're using both hands to play, unless you are able to swing some other part of your body over the controller), but this is more a toy than a serious tool, and Roland would have been much better off not including a D-beam controller and instead have a Foot switch for the leslie and a lower price tag.
Another strange feature is the Audio Input. It's OK, if you wanna mix some sound with the Organ while you play, but you can't even pass the external Audio through the Leslie simulation. For submixing an external stereo sound source to only take up two tracks on a mixing desk, it's possible, but a bit of a hassle, since there is no seperate control for the organ volume.
Another annoying omission is a dedicated perc ON/OFF button. You use the same button to toggle between 2nd, 3rd and OFF positions. I like to switch the percussion on and off frequently, and this is going to be a hassle.
All together, however, this is the best sounding organ module around, and though it's not cheap, it's still reasonably priced. I've been waiting for this since I bought a VK7 5 years ago, so in spite of the various problems (all showing a total lack of understanding of the basic needs of most organ players), I'm quite happy this unit has finally arrived...