I should have mentioned one other thing. The external back-up disks that I use are 2.5 inch laptop hard drives that I put into a reusable external enclosure. That way, they can be used as an external USB backup disk and, if necessary, the hard drives in them can be swapped out anytime. The bonus here is that if you use SuperDuper and your laptop hard drive fails, then you can simply take the back up hard drive out of the enclosure, pop it into your laptop (deceptively easy) and continue as if nothing happened*.
As for restoring through Time Machine, you're very correct in that you can use the program to do so. However, if your laptop hard drive fails and you want to restore through Time Machine, then you need to buy another drive, put it into the computer and then use the external Time Machine drive to restore. With SuperDuper! you can just swap the backup drive directly into the computer and you'll be back posting on iHub within 5 minutes (!).
And yes, SuperDuper and Time Machine can be used together. Although both are forms of backup, they have slightly unique niches.
Regarding my comment about use on laptops, my understanding is that changing the hard drive on an iMac is relatively cumbersome and not something people look forward to. In that respect, the convenience of having SuperDuper diminishes since you'll probably have to take it to an Apple Store to do the swap. In contrast, it's very easy on laptops as long as you have a 10 dollar set of screwdrivers. I suspect the new Mac Pro will also have easily swappable drives.
* Depending on when you made your last SuperDuper clone, some files may be out of date. Time Machine or another service like Backblaze can remedy that situation.
