While more advanced than ED-209, ED-260 was still plagued with performance issues. It couldn't even direct traffic without opening fire on civilians who made the smallest infractions such as U-turns, and upon illegal lane changes performed by panicked civilians trying to get away from the droid's overzealousness.
Dr. McNamara blames these performance issues on lack of funding from OCP, who would rather pursue the RoboCop program due to it's far more reliable success rate.
The ED-260a had additional features like treads built into the legs for faster travel, jet assisted jumps, and a "Rocket punch" attack by firing it's entire arm, which could return. It still had one glaring flaw in it's armor that allowed RoboCop to defeat it.