Using razor blades has some drawbacks...
1. It's not a good idea to place your hands in the tank any more than necessary, as it introduces dirt, soaps, oils, risks you for infection, and screws up your skimmer. Cleaning is a task that's easily enough done without sticking your hands in. You can wear gloves to mitigate this problem, but the gloves cost near as much as a scraper does.
2. Razor blades often come with a thin coat of oil on them to prevent rusting, which you don't want in your water. You can wash the blades and rinse well if you want though.
3. Razor blades can very easily slice right through the sealant in the corners, sometimes without you even noticing. You need to be careful.
4. It's hard on your hands, and if you drop one, it can slice through coral flesh on the way down.
Some people also say that because they are steel, they leech harmful compounds into the water, but I doubt that's a problem, it's not in the water very long, but once one starts to rust you should stop using it.
Not saying it's the wrong way, just throwing some things to consider out there. I'm also certainly not saying that the expensive bling bling scrapers are the answer either.