WD My Book Thunderbolt Duo
If price has been your biggest concern about a Thunderbolt storage device, and it should be, then the new My Book Thunderbolt Duo from Western Digital is worth the wait.
After teasing about it at CES 2012, WD finally released the drive, and it costs about $100 less than the 2big Thunderbolt from LaCie, which offers exactly the same storage capacities and RAID support.
Similar to the LaCie, as well as other Thunderbolt drives on the market, the My Book also doesn't come with a Thunderbolt cable, which will cost you another $50.
There is a small catch to the new drive's comparative affordability, however: it was rather slow in my testing, about the slowest among the half a dozen of Thunderbolt storage devices on the market. The reason for this is the My Book uses WD's Green hard drives, which are designed to use less energy but tend to run a little slower.
The drive is significantly faster than any other external hard drive of the same configuration that uses USB, FireWire, or eSATA. That said, it's still among the fastest external storage devices and will make quite a decent investment for those in need of Thunderbolt storage.