I'm not sure about the latest version of code, but on older code they are instantly unreversed and there is no ball save period. Also, when they revert back to reversed (assuming you've kept the balls in play) there is no warning. As you write, it would be better to have it like TSPP's Mystery Spot where there is a brief ball saver when you get down to one ball.
Quoted from Snailman:I didn't realize that. Does this instantly un-reverse your flippers in Flipper Frenzy -- and without a short ball-save period? That would really suck if you're in Flipper Frenzy, have your arms crossed over, ball(s) cradled on one flipper and shooting for the ramp with the other, only to hit this "good witch" award suddenly drop your cradled flipper and raise the other for a verbal-tirade inducing drain of your cradled ball(s).
Speaking of which, both Flipper Frenzy and No Hold Flippers desperately need a short ball-save after you drain down to one ball.