Barkeepers Friend has oxalic acid in it so it will work to remove rust stains. It is also an abrasive as Dale said. As such, I prefer not to use it on fiberglass unless I'm very careful not to "work it in".
The original "glass-top ceramic" electric ranges put out 30 years ago recommended BKF. It was and is great for getting burned crud off the smooth ceramic surface.
Trust me, the way I cook as a bachelor, BKF has come in REAL handy :lol: . I still have the original stove thanks to it. Now the oven is another matter altogether :roll: r !!
I've used it on fiberglass too.....just be sure to dilute it with water to a VERY loose and liquidy paste...almost a somewhat soupy...until you get the consistency that you need fot the task at hand. IT WILL WORK WONDERS.
BKF is good stuff. I have also had excellent results with Oxy Clean for general boat cleaning. I buy the tub size from wallmart and throw a scoop or two in with my boat soap. Oxy Clean is non-abrasive.