I have Bass tackles twinjector and it is designed to give you consistant results time after time. The two injectors fill at the same time and give even pressure when filling the mold thus you get a real even and uniform bait every time. The tip are held on by a pin so they dont fall off in the hot pyrex cups. With this system there is no pumping the hot plastic in and out just fill and shoot. I do not have a bears unit so I will not comment on that one.
Also the twinjector is available in two sizes around 6 oz and 12 oz. Plenty of plastic for the non production minded person. My large ones are on the way. I posted a video here when it first came out. The post also includes the bears unit video. FrankAs for needing the two parts you were asking about I think you would need to have both units to really know if you need them. Edited July 8, 2010 by Frank.