Product review (1 stars): Beware: Item Rusts
This stopped has 4 iron magnets in it, but the cheap plastic pieces used to cover the magnet aren't water tight. So water leaks into the stopper where rust builds up and causes the magnets to expand till the stopper won't fit in the drain to activate the garbage disposal. It's a cheap piece of s*** sold at a premium price.

I purchased a new one and will spray paint it with clear enamel to try and keep the water out; not something I should have to do myself for a $40 stopper.