Update: Added BareFeats performance testing information.
If there's one word I'd pick to describe Elgato's newest Mac peripheral, the Thunderbolt SSD external drive, it would have to be "minimalist." With this product, the company has delivered storage so simple that it's almost featureless.
The Germany-based accessory maker (best known for the EyeTV line of tuners and video capture gear) jumps into the slowly-growing Thunderbolt market with these two drive models, identical save for capacity: the 120GB unit retails for $429.95 and the 240GB unit for $699.95. Unboxed, the drive is a compact gray metal oblong -- no lights, not much adornment, and just the single Thunderbolt port dead center on the back. It feels quite solid and is about as heavy as a LaCie rugged compact FireWire drive.
Plug it in, and it mounts on any Thunderbolt-equipped Mac; it's thoughtfully preformatted as HFS+, since precious few Windows users would have any use for it. Note that the drive also requires, but does not ship with, a Thunderbolt peripheral cable -- so add that $40 to your net pricing. In use, it's fanlessly silent, although it does grow warm over time. You gain all the benefits of SSD storage, including no-moving-parts reliability and full resistance to magnetic field interference.
Given the premium price (not as steep as LaCie's TB external SSD, but that includes a passthrough Thunderbolt port that the Elgato drive lacks), what are you getting for the money? Standalone storage for your Mac that beats USB drives on speed; it also blazes past external FireWire 800 drives, for machines that have that interface option.
Update: BareFeats also performed tests on the Elgato drive with several different performance tools (AJA System Test, QuickBench & others) and saw dramatically better sequential write performance than I did; however, when they tested with the BlackMagic utility, they saw the same performance I reported. It is possible that the BlackMagic utility is doing something with write testing that is not optimized. BareFeats also noted that the Elgato unit is using a 3G SSD internally; when they replaced it with a 6G SSD storage module they saw a corresponding bump in speed.
Elgato cites an optimal data transfer rate of 270 MB/second for data reads in its testing. When I fired up Blackmagic's speed test utility, I didn't get quite that fast a show, but it was definitely respectable: 222 MB/s on reads, 112.7 MB/s on writes. Compare that to an external FW 800 1TB drive, which leveled off at about 80MB/s on both writes and reads. My MacBook Pro's internal SSD (an OWC Mercury Pro 6G), connected directly to the SATA bus, topped out at 281/163 read/write. Of course, none of these speeds measure up to the fastest rated SSDs out there.
One can't expect to do too much data sharing with the Thunderbolt drive, at least not until most of your fellow travelers also have TB-enabled machines. If you're looking for additional storage for your MacBook Pro or MacBook Air, it's fast and sleek; you're paying for speed and simplicity, but slower USB or FireWire storage can be had in much higher capacities for a fraction of the cost, which would be more appropriate for Time Machine backups or archival storage. For now, the Elgato drive is a premium option that's great if you have the cash -- but it might be overkill for most casual users.