Of the patents that they hold, most are expired.
Of the remainder:
U.S. Patent 6,164,942 (Rotary engine having enhanced charge cooling and lubrication) -- Expires on December 17th.
U.S. Patent 6,325,603 (Charged cooled rotary engine) -- Expires June 24, 2020.
U.S. Patent 6,450,445 (Stabilizing control apparatus for robotic or remotely controlled flying platform) -- Expires October 12, 2021.
U.S. Patent 6,808,140 (Vertical take-off and landing vehicles [Covers the current configuration of the M400, more or less]) -- Expires February 7, 2023.
So, of the four patents that remain valid:
* Two pertain to rotary engines, and are thus not of interest to anyone using any other kind of power.
* One is relevant to control systems for drones (which seem to exist off-the-shelf nowadays).
* One just covers the current configuration of the M400 vehicle.
* One expires in four months, and they all expire in the next 4.5 years.
