This was announced a few months back, and reasonably representative demos began showing up on YouTube a couple of months ago, but pre-orders only began being posted at Sweetwater and elsewhere quite recently.
This is the only device of its kind; Keith McMillen does not sell these directly under his own name. But maybe being patient will pay off, as success (quite likely at $1K) may lead to a larger version?
I consider 4.3 octaves ideal for marimba -- I don't much care for what happens with the competing harmonics in the lowest register when extending to 5 octaves. Vibraphone can get away with a smaller range, but 3 octaves seems too restrictive.
This is partially compensated for by allowing transposition in conjunction with the ability to move the unplayable "black keys" to adjust for such transpositions (or to create new tunings).
The tactile response is said to be excellent. Not too keen on not having a MIDI connection and having to use USB bus power, which is generally unreliable -- especially for extended periods. Two USB cables is a bit much to deal with. Not necessarily a deal-killer.
As someone who loves chromatic percussion, has owned several instruments in that family over the years and feels quite comfortable with mallets, this is quite appealing, but it would also cut into the budget for a rosewood marimba that gets more expensive every year I put it off (wood scarcity).
What would really be helpful, is to get feedback on player-instrument connection when triggering "heavy" libraries such as Soniccouture's vibraphone. And whether standard electronic keyboard pedals (sustain/momentary, and continuous/expression) can properly emulate vibraphone motor on/off handling and thus build technique rather than damage it when going back to the real thing.