I will never use another cleaning magnet in my life! I find they scratch up tanks pretty bad if you leave them in the tank all the time or get even one little sand grain caught in it. Even the coralline stuck in the magnet seems to scratch the glass!!
I just use the long handled scrapers, and find it's an easy job with the replacable blades. Just keep the blades replaced. I use a scraper that uses household blades so it's super cheap.
