Several quilters have said they were dull. I found if they are turned over sometimes its just one side that won't cut good. Also make sure you only have one blade. Sometimes two blades stick together in the package and you really have 3 blades instead of 2 in your package and you actually have two blades in youir cutter. The slot on the pricy blades don't affect anything. That is just something the companies put on their blades and it doesn't have any thing to do with them fitting.