I can only imagine that if it's a continuous BU, that it's always sending and receiving data, and that would imply to me that, yes, it will always load your CPU. How much probably depends on the packet size, and I'll try to learn a little more. There may be ways to perform backups at a scheduled time, rather than constantly, and that might be better. It may be easier to just plug in a new HDD and move it from the external to one in a bay inside the box, if you got room for it...

And, even though it's probably all secure, and everything, I don't know about storing my stuff with an online thingy. Just a thought...