I like the simplicity of the UI overall, but I'm always surprised when people go through the trouble to make certain interactions really fancy when the less fancy version would be both better for the user and easier to implement.

In this case, the little popover when I hover over a circle. As I move my mouse around the circle, the popover follows along on the perimeter of the circle, and I must hover over the (hopefully) tiny red piece to get the dropoff stats.

Given the small amount of data being shown in the popover, why not show me the stats for "continued" + "dropoff" in the same popover and just place it to the right of the circle? No fanciness needed, and it'd be more usable.