The choice of a binary asteroid was brilliant
Too large of a single asteroid target, and the effect would be minimal... too small of a single asteroid target, and measuring the effect might have large error bars...
But a small asteroid orbiting a large one is a perfect laboratory for the experiment... the period of the orbit is easily measured...
And if you were worried about minuscule chance the impact setting a small asteroid on a course that may eventually impact the earth, that is not really a concern if its a small asteroid orbiting a much larger asteroid.
The Impact energy was approximately the same energy of the Oklahoma bombing in the 1990's... about 3 tons of TNT... we have much bigger things we could throw at an asteroid...