I have used the ES on both a tech camera and XF, and it's a excellent feature, IMO probably the single best feature that Phase has produced for a long time, (since the IQ interface and LCD).
For long lens work, 100mm and out, it's a must have. It has fixed the slight vibration issues I was seeing with 300mm, 240mm and 150mm lenses. (wish I still had the 300mm now).
Once enabled, you will have one shot where the focal is fired, after that all remaining frames are silent, just the finish beep.
I have not found really any landscape situation where rolling shutter has effected anything in my shots either. So for movement of leaves, trees etc. not an issue and for water if anything it just adds to the effect.
Still working on trying to use it hand held, with the 55mm and 80mm, but it's a bit tricky in that respect.
As far as differentiation between brands offering 100MP CMOS , this is huge plus and should be given strong consideration.
Paul C