Flexible RAID support, no USB
The My Passport Pro is bus-powered, meaning you won't need a separate power adapter to use it. In fact, all you have to do is plug the drive right take it out and plug it right into a computer. And that computer needs to be a Thunderbolt-enabled Mac (all newer Macs support Thunderbolt), since the My Passport Pro, disappointingly, doesn't support USB 3.0. With this caveat, this is very much a Mac-only storage device. Why? In most Thunderbolt-enabled Windows computers, you can use the Thunderbolt port only for display and not storage.
Out of the box, the My Passport Pro's two internal hard drives are combined into a single HFS+ (Mac file system) RAID 0 volume. This means you'll get the most storage space, which is the total of the two drive combined, and the top performance. RAID 0 generally heightens the risk of data loss since if one drive fails, you'll lose data on both, but, you can easily switch to use the two drives in a RAID 1, or as two separate volumes. (Read more about RAID here.) You can do this by using Mac OS' included Disk Utility tool or the WD Drive Utility tool preloaded on the My Passport Pro itself. In all, the new drive is most flexible portable bus-powered storage device to date in terms of how you want to use its internal drives.
In general use, however, I'd recommend using the drive in RAID 0, mostly to take advantage of its performance. Just make sure that you use it either as a backup drive, or, in case you use it to host hot data, make a backup of its content regularly.
I tested the My Passport Pro in RAID 0 and it was very fast, restringing the sustained copy speed of 180MBps for writing and 170MBps for reading.
In fact, compared with other hard drive-based, bus-powered portable storage devices, it's the fastest. There are a few other portable Thunderbolt devices I've seen that are faster but they all use solid-state drives on the inside and therefore much more expensive while offering much less storage space.
The drive is also very quiet. During my testing process, it never became hot enough to trigger the ventilation fan. Note that if you use the drive in RAID 1 or any other setup, its performance will be equal to that of the any single internal hard drive, which is not exactly slow, but will defeat the capability of the Thunderbolt connection.
The new My Passport Pro delivers in all most all categories for a portable storage device: It's capacious, fast, very convenient to use and quite affordable. While it's not the fastest and most compact drive I've seen, the combination of what it has to offer more than makes up for these minor shortcomings. The SSD-based Elgato Thunderbolt Drive+, for example, while much more compact and faster, only has just 512GB of storage space and costs much more at $900.
All that makes the My Passport Pro the best portable storage device to date for mobile Mac users.