Pros: This enclosure houses up to 6 SDHC cards and stripes them together (a la RAID 0) as a single SATA II disk. It's completely fool-proof to operate: Insert the cards, and it works.
I have been using it for a few months now with six Transcend 150X 16GB cards (which, alas, DX doesn't carry). Read speed exceeds 150MB/s and write speed is roughly half of that. I have been using it as a replacement disk in a MacBook laptop. It absolutely screams, and puts other SSD modules I have tested to shame. Part of the reason for this is that it uses six stripes, whereas most SSD modules stripe only four modules together internally.

Cons: None, really.
The enclosure would work with less then six cards, but performance won't be optimal. Also, every time you change the memory configuration (i.e., add/remove a card, or change their order) the disk becomes unreadable. Not really a con, just a side-effect of how the hardware works.
I had initially believed using this would lead to quite significant gains in battery life of my laptop, but the improvement was not that significant. Instead of the usual four hours I was getting, I am now seeing about five hours worth of usage. Your mileage will undoubtedly vary depending on how much you actually use the hard disk in your laptop during work.

Other Thoughts: I am going to replace this enclosure with a 250GB/7200 RPM drive from WD (96GB is a little restrictive). This enclosure will be placed into a home-grown ZFS based NAS I built as an SSD cache disk, which is probably one of the best applications for it.
An important tip: Try to get MLC instead of SLC flash cards for the sake of long-term reliability, if you intend to modify the contents of the disk.

Bottomline: If you have a few bucks to spare and you want to get a tremendous boost in terms of disk speed as well as improve the battery life of your laptop, go for it.