First, the elephant in the room...
In my opinion the Iridium Core is far from a VST in a box. With that said, I have this question: If there were say 200 factory presets as apposed to 1700, would you still consider this a VST in a box?
The fact that the Iridium has about 1700 presets is a big plus. Yes, this includes a number of presets which you won't want to hear, but there are many good to great presets included here. One can always start with an initial patch, but many of the factory presets provide an excellent starting point from where you can tweak minimally to heavily in order to create a new custom preset, with ample opportunity to discover a "happy accident".
My biggest reservations for not quickly adding the Core to my studio was lack of physical knobs/encoders, and wondering if the sound would be too digital.
Firstly, after getting use to the Core's UI, I find it totally intuitive to operate this synthesizer. there are so many functions, and almost all are easy to find and manipulate various settings. I am glad that there are several knobs to work with, and for navigation, they function beautifully with the 8 push buttons above the main screen.
Yes, this is a very digital sounding instrument, but with the most power and options than any other digital synth I have worked with. For me, each of the 5 sound generators are very good, with major strength in wavetable and FM sounds. With little tweaking, it's possible to at least add grit to the digital smoothness; however I wouldn't say to the point of an authentic analog filter sound.
If it's purely analog that you want, then the Iridium Core is not it. The Groove Synthesis 8M will be released in Europe soon, and in a remarkably similar form factor package, (plus a few more knobs)! My ideal studio has both the Core and the 8M.
Top summarizing thoughts:
Excellent build quality
Intuitive and ease of use
No crashes or any issues in 30 days
Sound options; Arp, sequence, many presets
Mod matrix
Size (The price was also a minor initial sticking point, but the fact that you are actually paying a little more because of the required size form factor could easily be considered a plus).
Edit: Correction - The Groove Synthesis does not compare because of the highly disappointing cost; €350 more than the Core. I will stick with just the Core.