Not sure about the ReadyNAS ProBusiness, but my NV+ has a USB port that I can plug an external drive in to, push the backup button, and in just a little bit I'll have a drive suitable for taking off-site. The FrontView web interface has a simple way to configure what the backup button does. Very simple.
It also runs Linux under the hood, and I've been able to configure CrashPlan for off-site backups of some key files too.
I use the USB port as well and connect a USB drive to it. But I am a bit more paranoid, and I do a bit-by-bit comparison of every file that I copy, after I do the backup.
It also runs Linux under the hood, and I've been able to configure CrashPlan for off-site backups of some key files too.