I have the OptiBay (well, a generic version that cost me $13.00 from eBay), and it works great! I have my storage drive in that bay and my SSD in the original HDD bay. The only issue I have ran into is if you want to Bootcamp, you need to put your original SuperDrive back in to install. After install, swap back to the way it was. Maybe you can use the MacBook Air SuperDrive to solve this, but a USB flash drive or a regular external DVD drive will not work.
Other than that, try to find a generic one (not Hong Kong), as $99 is a bit much for one.