It reads very fast; about 1/150sec too to bottom.
It’s slower than an a9’s mechanical shutter moves (roughly 1/300sec top to bottom per imaging-resource), but 2-3 times faster than most electronic shutters (also per imaging-resource).
So a greater chance of rolling shutter but not by much. Yeah...I'll retract my "meh" comment. There are some caveats to 20 fps on the A9 (lens; e-shutter) but it's still impressive.