In a thread on KC, someone asked about the KBP4 and how it behaved. Here's my shortish answer in more detail than I gave over there.
First off, I moved this long note to CL because the KBP4 is not a keyboard in the traditional sense, even though it looks like one. It's an MPE controller that uses a traditional keyboard layout to help players focus on new playing techniques without learning new fingerings. It occupies a space between what traditional keyboards can do and what a full-on MPE controller can do, although it's much more close to the latter.
The keys on the KBP4 are made with KMI's patented "Smart Fabric". This is a very sturdy pressure/impact/position sensing material that can be cut and implemented in various layouts, under key-shaped surfaces made of lightly textured (not very slippery) silicone. They have a slight give under the fingers, but there is no mechanical movement. In fact, the KBP4 has absolutely no moving parts to break, not even a power switch.
Connections include two minijacks for pedals (adapters included), micro-B USB for computer connection, and mini-B USB for KMI's little MIDI Expander box so the KBP4 can be used standalone with hardware.
The keys are ever so slightly shorter and narrower than those on a traditional synthesizer: if you were to hold a KBP4 up against a standard MIDI synth (as I've done), you would find that the KBP4's 48-note keyboard (C to B) is about as wide as 44 notes (C to G) on a conventional keybed. There are four assignable ribbon controllers across the top of the KBP4, which can be assigned to functions like pitch bend (global vs. the per-key control), modulation/CC, octave selection, or program parameters.
While the top panel and base are plastic, the actual chassis is solid metal and fairly heavy. This turned out to be a vital element in the design, as the KBP4 requires an extremely rigid frame for the keyboard to perform reliably.
The companion app to edit the KBP4's settings runs on Mac, PC, or on any web-capable device using a browser-based editor. You can set up the performance of the device, map multiple commands to multiple surface, and fine tune the behavior of each key if you wish. The patch management system is a little bit funky, and I'm still wrapping my head around precisely when program changes are saved and/or transferred to the hardware from the software. It all works well enough, but there's an order of operations that I don't quite get yet.
In terms of playing, the KBP4 has a very interesting feel. It's not as squishy as the Joué or ROLI Seaboards, not as stiff as the LinnStrument or Morph, and very sensitive to the touch. You can (and must!) play with a very light touch, and of course you can't rest your fingers on the keys without activating them unless you set the action thresholds appropriately. A friend of mine who has RSI and arthritis has become very intrigued with it, as it may allow him to play keyboards without further damaging his hands.
It's not a perfect solution -- some folks will miss the ability to do long pitch bends up and down the keyboard rather than simple side-to-side wiggling for vibrato, which is ideal on this action -- but it shows a lot of promise, and I plan to get more into it as my schedule permits.
Please feel free to hit me up with any other questions!