After completing assembly, it looks like you need to run both when using it as a slicer as the tenderizer is the only portion with a shaft to link into the motor of the grinder. There are then gears on the end of both the slicer and the tenderizer that turn the slicer using the shaft from the tenderizer. If any of that makes sense with my lack of engineering background explanation.
They must sell a jerky slicer attachment with a shaft on the end of it to go into the motor as you can buy this unit as a standalone slicer, a standalone tenderizer, or a combo kit like I purchased.