Should be, but that too is a great question, they tend to use the Chutes on landing, and we have very seldom seen the dorsal brake deployed, but once they are operational???? What the dorsal brake likely accomplishes if it does what it is supposed to??? is increase drag in the landing configuration, so you 2may carry more power, and "set" the aircraft in a position where it is easier to "flare" the aircraft just prior to touchdown.
For instance in the C-172, It is easy to flare with no flaps up to about 20 degrees of flap, once you go from 20 to 30 or 40, the aircraft takes a much more pronounced pull, and a lot more finesse to get a nice flare and touch down. In foact when Cessna introduced the C-152 to replace the C-150, they limited flap travel to 30 degrees for just that reason. So the dorsal will give you a positive pitch angle to the relative wind on approach, then the flare is just managing your airspeed and slight tug aft on the stick to break the decent and hold it off momentarily until it sinks slightly to touch-down.
They really don't seem to slow the J-20 as much as some other fighters on flare, as in the light test configuration, they are not actually having to operate it with-in the narrow aerodynamic envelope that they will once it begins to approach max gross wt.
