The fast versions uses a magnet in the can bottom which keeps it from flying across the platform. The slow one has no magnet on the can. Mixing them can jam one I've heard, or for sure stop a magnetic can from going deep enough onto the platform when ejected from a slow toss or allow a non magnetic can to go flying with a fast eject.
If lettering is gone, I think you can classify the versions as a long scale car for slow, and shorter, maybe semi-scale for the fast eject. I'm not 100% sure, just an observation of memories.
