Justice droids were used years before the Clone Wars, and were so successful that they were reproduced by the Galactic Empire during the New Order. They were both strong and durable, and thus reliable to use.
One of these droids was the Imperial assassin droid 2-124, that was captured by the Rebel Alliance. The droid escaped and killed a number of Rebel and New Republic officials over the years. It was placed in GeneralAiren Cracken's confidential New Republic Intelligence brief listing the top fifty most dangerous beings to the New Republic.
An Iron Knight using the body of an Ulshos Justice droid.
Some Uulshos Justice droids joined with Force-sensitiveShard to form Iron Knights. The combination of a Jedi's use of the Force and an assassin droids skills made them deadly combatants.