Not quite prohibitive, but almost

- The USB power cable is useful for self-powered drives.
The card works without this cable with any hardware that has own power supply. The cable becomes necessary for the mini HDD 2.5 "USB key of high consumption, etc ... But not surprising that side, all Cardbus / ExpressCard are like that.

- Works with Windows 7 (SP1) with an older version of the driver (v2.0.4.0).
The current link (at the date of this comment) is as follows
[...]
If the link becomes obsolete through the "Frequently Asked Questions" (FAQ) of the product and look for "Why the USB3.0 external storage devices (eg harddisk) can not work Properly with the TS-PNU3?".
The drivers are available on other sites by searching for "Renesas USB3 drivers" or "Renesas USB3 Host Controller Drivers"; they are not specific to this card or developed by Transcend: These are drivers for the chip NEC / Renesas used the card.

- No true plug & play.
When the card is ejected, I have to manually refresh the device manager for the drivers disappear from the list. Otherwise the next insertion equipment connected to the card are not recognized.

Finally the card works, but not what one would expect from a hardware such today: minimalist support (lack of drivers, incomplete information), unusable for a layman, fragile. The fault lies with Transcend for the service, and NEC / Renesas for reliability / compatibility of the product. If I had to make my purchase, I will look for a card that uses a different chipset than the NEC.