I've had problems doing that; the backup doesn't always run, and it often decides to blow the entire backup away and do it again from scratch.

The first problem could be down to the fact that I don't use the Mac that often: my daily computer is a Linux Mint desktop; the Mac is only for when I'm out. It takes weeks until it actually gets around to installing updates as well (this is something that Windows Update gets right, imo).

I might just get an external disk for the Mac instead.

I've looked at backup for my NAS, and I still haven't come up with one that I like. Currently all of my important files are on a Windows 2012 box, and I use BackupAssist to external disks for that.