Activation of Coasting is very noticeable. You feel the transmission disconnect and a freeing up of the drivetrain. But often and somewhat annoyingly it is on a gentle decline so the car immdiately is starting to speed up, so you can never be in coasting long because you require to operate the brake pedal and coasting disconnects. You feel the reconnect slightly less than what a gear change would be....it all happens very smoothly. I don't notice the drop in revs particularly, it's already in Eco, the exhaust is quiet, there is already road noise at 80kmh...it's dropped away but the change rather than noise is more noticeable.
The point I would make about putting the drive system into Eco for the other poster is that by continuing to change between them all and expecting coasting to engage when you predict it it probably won't happen so leave it where it is in Eco.
Because I drive in Eco 99% of the time and only give it an occasional squirt in Custom,, I notice Coating engage often when I am driving. Typically its after 20, 30 minutes of driving, 80 kmh speed zone, straight long shallow decline...it may go to coast mode.