Looks like MCE just updated their website, albeit it's just as confusing:
Communicate Natively
Speaking of communications, your Mac won't even mind that the OptiBay Hard Drive is now connected to its optical drive connector. It recognizes it as just another hard drive connected to its ATA bus, or SATA bus in the case of MacBook Pro and MacBook Unibody systems, and communicates with it just as it would any other hard drive. Remember, you have a Mac where stuff just works!
So from what they're saying, the MCE optibay connects to any Macbook Pro via (the Macbook Pro's) SATA bus. Explain this one.
http://www.mcetech.com/optibay/
Communicate Natively
Speaking of communications, your Mac won't even mind that the OptiBay Hard Drive is now connected to its optical drive connector. It recognizes it as just another hard drive connected to its ATA bus, or SATA bus in the case of MacBook Pro and MacBook Unibody systems, and communicates with it just as it would any other hard drive. Remember, you have a Mac where stuff just works!
So from what they're saying, the MCE optibay connects to any Macbook Pro via (the Macbook Pro's) SATA bus. Explain this one.
http://www.mcetech.com/optibay/