The biggest reason is that udev rule is "automatic" -- every time a new device is connected (or discovered during boot), udev will process all the rules files so you don't need to do anything manually.
mknod creates a new block (or character) device file, but you already have one --
/dev/sdd so you don't need to create a new one, you only need a symlink to it (which is what udev does with the
If you don't want/need the "automation" part of udev and are ok with running a command manually every time you boot or connect the device, I suggest you still shouldn't use
mknod but create a symlink instead.
If all you want is a nice (and stable) "path" for the device, I'd suggest setting label for the filesystem or partition and then you can use one of the default symlinks created by udev in
Note that udev is also used by other system tools that work with storage so if you create the symlink with udev, these will know that it is a symlink to that device. This might not be true with manually created nodes (but for example
lsblk is smart enough and if you run
lsblk /disks/QUORUML it will show you