The latest innovation from Tom Kuhn, released 2014. Yo-yo is configurable for either responsive play (you tug on the yo-yo to return it to your hand) or non-responsive play (you create a string bind to return the yo-yo).
Machined out of specialty aircraft aluminum by CYYC (Chico Yo-Yo Company).
The successor to this yo-yo was supposed to be the SB-4 Cobalt. Preorders for the blue yo-yo began in April, 2015. According to the Tom Kuhn Custom Yo-Yos website at the time, the yo-yos were to ship in mid July 2015. Unfortunately, as I later found out through a primary source, not only did the yo-yos not ship, but the entire project was cancelled due to low interest/orders (this note added September 5, 2015). Very disappointing to say the least; I was looking forward to its release for a long time.