What is the safest way to perform backups of my partitions?
cat is a very bad idea here. If you really want to make a backup on partition level, rather take a look at dd. What you probably want to do is something like

dd if=/dev/mtd/mtd0 of=/sdcard/mtd0.image


For more details, you might want to consult the dd Man Page. Remark: I'm not sure whether the dd shipped with Android supports the full list of options, so you might have to try out.