He's very efficient, if maybe flashy (5)
I believe the answer is:
robot
'he's very efficient if maybe flashy' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'he's very efficient' is the wordplay.
'he' becomes 'Rob'.
'very efficient' becomes 'ot' (I am not sure about this - if you are sure you should believe this answer much more).
'rob'+'ot'='ROBOT'
Can you help me to learn more?
(Other definitions for robot that I've seen before include "Soulless worker" , "Computer-controlled machine" , "Mechanical worker" , "Humanoid machine" , "programmed servant" .)