With occasional recycling of the space, there's no danger that I'll run out of backup space in the near future - it's five times the size of my internal hard drive, which I haven't got past about 70% full in two years of use.
The OneTouch gimmick is that there's a big button on the front of the drive which you press to kick off a backup using the bundled Dantz Retrospect Express 6.0 software. You can configure the button to launch something else if you prefer and, as I quickly discovered, you can configure Retrospect to do scheduled backups, which I reckon will be still more useful than the one-button approach I expected to have to get used to.
The first backup seemed a bit slower than I had expected, but I discovered that this was down to a deliberate feature - the first ten times the drive is powered on, it does extra hardware verification on every write!
I left the backup software doing its own verifying when I went to bed and, as seems to be traditional with all backup software the first time you try to use it, I awoke to find an error message waiting for me in the morning. Having checked the log, I think this was just because it tried to kick off the first scheduled backup immediately upon finishing the one I had started manually and couldn't cope with the handover. As this is not a circumstance that's likely to happen again once the schedule is established, I'm not too concerned, but we'll see how it goes.
Despite being a professional developer who should, of course, know better, this is the first time that I've had a relatively satisfactory solution for regular backups, so I'm looking forward to an increased sense of security. So long as I don't have to fall back on that non-existent off-site backup...