Let me preface this review by saying that I'm a big organ fan, I love them and can never have enough organ sounds. The ZR1 though doesn't get much use from me anymore. To me it just sounds a bit cheesey, more like the kind of organ you'd hear at a funeral parlor as opposed to a real tonewheel, or combo organ. That being said, none of the organs in my collection sound quite funeraly either :) . As far as freeware goes than the ZR1&3 are probably the best freeware organs on the VSTi scene, but neither is going to quite nail that real tonewheel kind of sound, nor does either sound very much like a true combo organ. Also the bass on it just seems kind of muddy, and not at all well as well defined as I'd like, while the high end just sounds a bit cheesey without that metallic harmonic quality you'd expect from a tonewheel organ. The GUIs are functional, but within Sonar always seem to be resetting the graphics in a wierd way which makes me think the plug-in will crash at any given moment (but it hasn't yet). If you're not one to use organs very much in your music, than the ZR1 may fit the bill nicely, but if your inclined to use them frequently going for something like DaOrgan or Combosister (depending on which organ flavor you want, or both) would probably better suit your needs even on a tight budget. I haven't found a place for the ZR1 just yet, but it's still going to stay around on my hardrive just in case.
At 16 april 2002 it's been replaced by ZR3... itself discontinued at 19th december 2005 being replaced by AZR3. So the version to use is AZR3 (and its real page is not the in the link of KVR, it is here).