Hello bud,
It might be worth your while plugging the duo in and seeing if there is a image already installed on it, there could well be although it might just be the original Vu image.
In answer to your questions,
Yes you can flash the duo straight out of the box no probs, but I would update the bootloader first just to be on the safe side before you flash on any of the latest images.
No real need to backup the original firmware that comes with the duo as this can be flashed back on at any stage if you prefer it.
There is a newer version of the full backup you have chosen available here: http://linuxsat-support.com/vu…-full-backup-mckee25.html
Once you have flashed that on then you can set your own preferences. Also have a look at the Vix backup's on the forum, well worth a look.
Good luck and let us know how you get on.