Looking for MacBook Pro compatible true USB 3 ExpressCard 34 cards at USB 3.0 speed (or at least a few Gb/s) on any brand USB 3 drive in Mac OS X
Looks like the CalDigit is the best option - there is no deliberate proprietary lock down with their USB 3.0 cards for Mac/Windows.
I emailed and then telephoned their support in the US, (from the UK!):
They have tested it on other brands as well as their own. They sensibly say cannot guarantee every drive will be compatible, but nor are they saying other brand drives won't work.
It is possible that a given USB 3.0 drive will work with the CalDigit ExpressCard 34 SuperSpeed USB 3.0 on the Mac at speeds at a large fraction or meeting USB3.0 speeds i.e. 1 or more/several Gb/s or at least far higher than USB2.0.
The only instances they are aware of are where a bus-powered very large capacity i.e. >1Tb (at time of writing) drive draws too much power due to the large number of platters being spun. (I don't work for CalDigit).
Update:
With pleasure, I can report that the Samsung S2 1Tb 1.0 Tb USB3.0 Superspeed drive does work with the CalDigit ExpressCard 34 USB3.0 Superspeed with MacOS Lion 10.7, at noticeably faster speeds than when it is plugged into one of the Mac's built in USB2.0 slots. When same Mac is booted into Windows 7 64 bit pro via bootcamp, the drive also works. CalDigit supply a Apple MacOS driver and Windows driver for their card, downloadable from their site, caldigit.com
So, in conclusion, it looks promising that CalDigit's CalDigit ExpressCard 34 USB3.0 Superspeed will work with at least several brands of hard drive. That was their intention to implement USB3.0 in such a way to support any USB3.0 drive, though they cannot test every drive manufacturer due to time and resources. Once again, I don't work from them. Though I am pleased with their approach rather than Lacie's locked down approach with Lacie's MacOS driver only supporting Lacie's brand.
Update
See also my other question and answer: How to get ExpressCard 34 USB3 working on Apple Mac OS X 10.10 / 10.11 + (via 1 or more of: kexts,signing or choosing compatible models/chipsets)?