4. You can use it on tile and fiberglass in the bathroom as well.
I do it on mine now and all I have to do to clean it is wipe it with a cloth. Just be very careful not to do the bottom of the tub like I did once. It was slippery as glass and it took a half a gallon of pickling vinegar to get it all up. Not my brightest moment.
It's not a slam at you when people are rude, it's a slam at the people they've met before. ~ F. Scott Fitzgerald