Original script backups only part of filesystem, for example zImage (which is kernel image), but not /lib, where kernel modules are located (and they are unique for each kernel version/build), as you can see in init scripts some custom module loading (for example in usbcamerasetting.sh) happens, restoring only image from newer or older firmware version can lead to non working unit or parts of unit, so i suggest to backup full fs and explore it if you are interested. There is 3 interesting mount points:
/dev/root 3.0G 306.5M 2.5G 11% /
/dev/mmcblk1p2 3.0G 306.5M 2.5G 11% /media/mmcblk1p2 (this is rootfs ( / ) in fact)
/dev/mmcblk1p1 499.7M 7.5M 492.2M 2% /media/mmcblk1p1
I've attached my version of backup script, it'll tar (without compression for speed reasons) all this 3 mount points, you can exclude one of / or /media/mmcblk1p2 if you don't want two copies.
Script can run few minutes, executing instructions are same.