This is not a breakthrough capacity hard drive; it's an external storage device offering two smaller drives you can configure in mirrored or striped modes.
By default the product ships in RAID 0, appearing as a monstrous 931GB drive once it has been formatted. Although RAID 0 should offer good performance, USB 2.0 could well be a bottleneck. It's therefore handy that the product comes with support for the FireWire 800 interface, offering theoretical speeds of 786MB/s.
However, the Pro Edition possesses horribly noisy fans that start up at seemingly random times. This is a nice way of adding 1TB of storage, but the bulky box and abundance of wind noise make it difficult to live with.
Fitting 1TB using run of the mill internal drives is cheaper and quieter than this, so it's only worth the price if you're desperate for massive portable storage.