Thanks, again, for chiming in.
I checked into the G-Tech products. Some reviews on Amazon. Pretty split opinions, which is to be expected. The concern for me, however, is the nature of the complaints (i.e. product failing in 1 to 2 years and no recovery of data possible).
In my digging around OWC, I found some "Buffalo" units which looked like the ticket. However, there are multiple complaints about the Thunderbolt ports failing and abysmal Buffalo follow-up customer service.
I do not have much to store, but what I do have is valuable to me. I have had the Apple Airport/TC since 2006 and there has never been an issue with it. I have even "secure erased" it a few times over the years and it always resumes to the expected behaviour with Time Machine.
OWC offers a 1TB Firewire 800 portable which is very similar to the 250 GB Firewire 400 external hard drive I got in 2008. It, too, has been without issue and I still use it today (with a 800-400 adapter cable).
So . . at this stage, I will likely just stick with my usual routine of the Ethernet port for the full backup and then Wi-Fi for incremental backups. Slow, but at least it IS reliable.
I, optimistically, was hoping to find a Thunderbolt HD around the $200 mark that I could count on. Bummers.
