I used all 3. Not sure if the pictures show them all. I put one in the Threshold deployment zone (nothing said I couldn't), by the objective, and by my own deployment zone. I felt a bit dirty about it, but I played the Scrawny Ones badly.
You should use them to go after minor civilians or already downed agents and characters. They aren't strong enough to defeat a Threshold character or agent on their own without some very lucky rolls.