Here's my understanding.. I think these are set up to "work like traditional slingshots" in the sense that the switch on the rubber is detecting when to fire the slingshot. Only instead of a kicker to push the rubber, the magnet pulses to pull the ball away from the rubber. So in that sense, the magnet probably won't pull the ball except in response to the slingshot switch being hit.
Multiball would definitely be unique as the magnet would pull all balls in its vicinity toward each other.
As I'm in on a premium, I'm personally looking forward to seeing a gameplay video.