The only downside I found to the ES on IQ3100 was the need to shoot the dark frame (put a lens cap over the lens or similar) anytime the shutter speed was changed. Longer exposures with larger filters like 100 x 100 or 150 x 150 was taxing. Each time you changed the shutter speed, you were asked for a new reference frame. I never found a way to avoid this on the 3100. Same issue on the 3100 and XF as any exposure 1 sec or longer had to have a mandatory dark frame. Again for photographer working a series 30 seconds or or even 10 seconds, having to wait an additional 10 seconds or 30 seconds before you could fire again was problematic. In shots where I wanted to pan, at sunrise, the wait at times caused problems due to movement of the clouds over the wait period.
As for the other question, I would still get a copal if you can, just adds a bit more value to the lens and ability to resell if necessary.
I never found any issues with movement with the ES on the 3100, leaves, branches etc. net no issues in outdoor shots. Like previous posted something moving fast like a car, bicycle, motorcycle etc will have classic rolling shutter or propellers. The ES on the XF allowed for much more detailed shots for me with the 75-150 and 240 LS lenses, on Tripod. Before the ES upgrade, motion blur was always a problem even with the vibration feature of the XF.
Paul C