The VCI works so well for what it does, however what it does has got to be what you want for your investment to be sound. The VCI is expensive compared to the price-cut S4 and some of the cheaper midi gear out there. I feel that without intending to customize the VCI then the price is a bit too steep imo.
As for the controller its build quality is immediately apparent when comparing it to other gear. Everything looks great and feels very solid. I feel that the VCI has a perfect size. It's small enough to be portable and fit alongside other gear. Yet despite it's relatively small size everything feels easily usable. The knobs have plenty of space between them and they're big enough to use in quick-finger moments. On many forums some people have expressed disapproval in how quickly the jogs work with traktor. Personally, I have latency lowered to 13ms and I find there to be no noticeable latency between jog manipulation and response in the Traktor software. I am using an i7 powered machine and i'm sure this makes a good difference.
The sound quality is excellent and with a 24bit soundcard that's no surprise. I don't have the trained ear of a veteran producer/engineer but I can feel the clean signal and clean powered volume noticeably when pumping 24bit .wav songs.
The setup is fairly simple for Traktor. The gear flashes firmware up and down very stably and should you mess something up it's usually a quick fix. The VCI support community is by no means as large as the S4's, but it's good enough to support confidence.
Only gripes are that my first controller didn't work properly. On the first-shipped controller the jogs wouldn't properly register pressure. Excellent customer service paid for shipment back to their shipping facility and another VCI was shipped to me in a few days. My only other gripe is that the large red filter knobs each give different levels of resistance when used. This has evened out with some use, but I think at this price such small issues shouldn't exist.
Overall I love this piece of gear and it beckons to be in a relationship. With reliable soft care I'm sure I'll be using this piece of kit for many years to come.