Like Mr. Dave said, the device is sub-ohm capable meaning it will fire coils rated less than 1.0 ohm.
So technically, it will fire a 0.99 ohm or less coil thusly it can be advertized as a sub ohm device which has become quite the Buzz Word in the last 8 months or so with regulated devices and tanks.
Your device is good down to 0.40 ohms, Anything above that is fine.