The used CineMilled PRO Dovetail for the Freefly MoVI M5 is designed to replace the dovetail plate that comes with the MoVI M5 to allow you to counterbalance front-heavy loads.
It’s slightly longer and offers a series of 3/8"-16 threaded holes across the back that support optional CineMilled counterweights (CM-070 and CM-080), which are available in 1" and 2" sizes and are stackable. It’s also T-shaped so you can mount the weights offset in cases where that would better balance the camera.
The MoVI M5 is generally limited to small cameras, and the PRO Dovetail allows you to use larger ones by enabling you to counterbalance them. Alternatively, it also allows you to balance very lightweight cameras, as light as a GoPro, by adding the optional weights on top of the plate.
Just like the original plate, the PRO Dovetail also provides the threaded mounting points on the front for attaching the rod support bracket that comes with the MoVI M5.