Very small differences, the main one is the pump, 9005 used the 9005.040 pump which was the older Turbelle style, the new 9006 uses the 9006 Turbelle ejet hydrofoamer. Both have unidirectional impellers and the older Turbelle had a mechanical clutch to get it going the right way and the new one uses an electronic system, this mainly improved the noise of the pump. Also, the 9006 comes with a magnet holder, 9005 had the old "erector set" rail holders.