How much of a premium will you pay for SSD? The SSD drives (with FireWire 800, FireWire 400, and USB 2.0 interfaces -- see port photo below -- and a 64MB cache) go for US$299.99, US$479.99, or US$779.99 respectively for the 64 GB, 128 GB, and 256 GB versions. Similarly sized hard drives, also with the triple interface but smaller caches, cost US$99.97 for an 80 GB 5200 RPM drive, US$109.99 for a 160 GB 5200 RPM drive, and US$134.99 for a 250 GB 7200 RPM drive. That's a US$645.00 premium for the 256 GB drive! Is it worth the extra cost? It depends...
The benefits to SSD that I alluded to earlier are speed and durability. OWC states that booting from an SSD can be up to 2.5 times faster, and the seek time for accessing data can be up to 120 times faster compared to conventional hard drives. In terms of durability and reliability, the SSDs can take up to 4.5 time more of a physical shock and still keep running, and can last for up to 1.5 million hours of reliable usage, which is about three times what a conventional hard drive can endure.

SSDs also work in more severe temperature extremes, are completely quiet, and the lower power draw means that your laptop is going to stay up and running longer if you're connected to an SSD than if you're using a conventional external hard drive.

The Mercury On-The-Go SSD comes with OWC's usual bundle of software, which includes Data Backup 3, Nova Backup, and SpeedTools Utilities. Most Mac users, however, will probably opt to simply use the drive with Time Machine or a more popular backup utility like SuperDuper. When you pop open the box (see picture below), there are also a full printed Owner's Manual and Windows formatting instructions, a USB 2.0 cable, a FireWire 800 cable, and a FireWire 400 to 800 adapter cable. Since the drive is bus-powered, there is no AC adapter to lug around. One other nice touch -- OWC provides a leather carrying pouch with a soft lined interior for carrying the drive and cables.
The drive itself looks a lot like any of the other Mercury On-The-Go drives, meaning that the drive mechanism is encased in a clear plastic case. The SSD has aluminum cooling fins on the bottom of it, which is probably why I never found the drive to get more than just slightly warm.

My real-world testing involved two steps: performing a first-time Time Machine backup to the drive and reading / writing a video folder from the drive. I wanted to compare the speed of the SSD to a conventional hard drive. For my testing, the throughput was limited by my choice of the USB 2.0 cable, since I was using my MacBook Air as the test platform. The conventional hard drive I used for testing was a bus-powered USB 2.0 drive from Western Digital.

One thing I found a little annoying was that there is a power switch on the device, which (after reading the manual) I found out defaults to a setting that assumes that you have an AC adapter plugged in. Since I didn't, the drive didn't respond when I plugged it in with a USB 2.0 cable. After noticing the switch position information in the manual, I quickly resolved the non-issue and the one blue LED on the front of the drive began to glow.

Here are the results of my tests:

Time Machine Backup - 39.9 GB (SSD): 3 hours, 55 minutes, 02 seconds
Time Machine Backup - 39.9 GB (Conventional Hard Drive): 2 hours, 41 minutes, 50 seconds

Write 658.1 MB - 122 items (SSD): 32.6 seconds
Write 658.1 MB - 122 items (Conventional Hard Drive): 31.7 seconds

Read 658.1 MB - 122 items (SSD): 35.9 seconds
Read 658.1 MB - 122 items (Conventional Hard Drive): 32.5 seconds

So, what happened to that speed advantage? As I noted earlier, both drives were limited by the choice of a USB 2.0 connection, which explains the similar times for most of the tests. OWC's own benchmarks show that USB 2.0 read speeds for the drive max out at about 36 MB/second, while write speeds are limited to near 30 MB/second. For FireWire 800, those speeds are close to 82 MB/second for read, and near 78 MB/second for write.

These speeds are similar to what you'd see with a 7200 RPM conventional hard drive. OWC's benchmarks show that the 250 GB OWC Mercury On-The-Go drive at 7200 RPM has a 74 MB/second read speed and about 73 MB/second write speed. That drive, priced at US$135, is approximately the same capacity of the US$780 SSD drive.

To me, one of the most impressive features was the absolute lack of sound from the drive. I have a very noisy OWC Mercury Elite Pro - AL 1 TB drive on my desktop which I can literally hear from across the house when it's chunking away on a Time Machine backup. I was not able to test the durability of the drive, although I did drop it from the limit of the USB cord's length onto my desktop multiple times during the backup without a hiccup. I also like the way that OWC recesses the ports on the back of the drive so that they're less likely to be damaged in a drop.

Who are OWC's external portable SSD drives for? Mac owners with deep pockets who like to have the latest technology, people who need a durable drive that can withstand drops without a glitch, folks with extremely sensitive hearing who don't like the rattle and hum of conventional hard drives, and people who want the maximum in speed from a portable drive. If you're going to use one of these drives, I would recommend using a FireWire 800 connection to make sure you get the best possible speed out of the drive. If you only have USB 2.0, you're much better off purchasing the much less expensive 7200 RPM conventional drives from OWC.

While I am impressed with the SSD, the current prices and capacities aren't enough to get me excited about buying one. I look forward to seeing what OWC makes available in terms of SSD capabilities in the next few years.

FTC-required legal mumbo jumbo: The Mercury On-The-Go SSD storage solution was provided to TUAW for the review purposes and has since been returned to OWC.