I came across the VB3 a while ago as I wanted to get back to using organ sounds in my music (Had sold my old "pre MIDI" Korg CX3 already a few years ago).
User Interface: Anyone who ever played a real organ will feel at home here: Draw bars for two manuals and pedal on the bottom, above that controls for vibrato/chorus, percussion, overdrive and the Leslie. All well designed and not too small. A large amount of additional features for tweaking the organ are in Preset/Global menus.
Sound: Just one word: Fantastic! It roars and sings almost like a real thing, with the right amount of imperfection. But you will need to play this as a real organ, using controllers for swell, Leslie speed, and maybe play with two manuals or manual split to really achieve a living Hammond sound - this is not a synth that will create a sound scape by simply hitting a key once. I have used the VB3 on my recent CD in several tracks and noticed also how well it fits into the mix with minor EQ adjustments.
Presets: VB3 comes with 32 presets, covering the range from Gospel,Jazz,Funk to Rock. They are a good start to get you into your own preset design. You should also invest some time in adjusting the options to your personal preferences (tone wheel leakage, type of Leslie etc.) The only presets that did not convince me fully are those emulating the Farfisa and Vox organs.
Features: As mentioned above you can set and tweak almost everything that is relevant for a Hammond sound, specifically in the Global options which give you control of your organ's age and characteristics. I like that the features are focusing solely on what is relevant for an organ, no multi effect, delays, bit crushers or such included.
Value for Money: The VB3 costs 49 Euros which makes it a real bargain. Besides, it sounds better than some other emulations that have a price that is 2 or 3 times higher.
Support: I never had problems with the VB3, but had contacted Guido to give feedback, also on the ZD6. He was very responsive and open for suggestions.
Documentation: Good and sufficient information about all features. It is nice that you also get some background info about how things function in a real Hammond organ (tone wheels, scanner vibrato). Also tube emulation and different speaker cabinets are well described.
Stability: Never had any problems with VB3 so far, playing it live or and while recording with Reaper and Cantabile. CPU load is okay, considering that it is a quite sophisticated emulation, not a sample player
In a nutshell: If you are looking for a real organ emulation this is probably the best choice, and all that at a ridiculously low price. One comment I would like to add: This is not shareware or freeware, but a professional product showing that the developer put a lot of effort and knowledge into it. One need not do glossy 4c ads to be a professional vst developer IMHO ;-)