I agree with both suggestions. I will only use a single edge razor blade to clean my glass tanks now. I really scratched up my 220G using a Mag Float and a sponge cleaner. It didn't matter how careful I was, it only takes a couple grains of sand to do damage.
come take a look at the front panel of my 55g (now my sump) if you don't believe me...
If you're careful with the mag scrapers and pay attention to whats going on, you can do pretty well without causing scratches. I do have a plastic handled plastic scraper that works pretty good to scrape the glass near the substrate when I don't have the patience to do it with the mag scraper.
I have five flat glass tanks, and use a single edged razor blade, and for rough surfaces, I depend upon Hypostomus plecostomous (Plecos) Work good, last a long time! And since I have Malawi Mbuna, the fish eat the scrapings!