The HeadONE and Pan PRO can either be used as a head unit on a slider, dolly, or jib. The Pan PRO can also be used underneath JibONE as a jib panning head, but the HeadONE cannot be used in this way.
The HeadONE can be connected to a second HeadONE via Tilt Kit v2 for pan and tilt functionality, however, the Pan PRO can only be used for panning, it cannot be combined with a second Pan PRO for tilting.
Lastly, the Pan PRO has a stationary target tracking feature while mounted on top of a slider, dolly, or jib. The HeadONE does not have this feature.