The Universal Drive Adapter allows practically any hard drive (or optical drive) to be attachable to your current Mac via USB. Because the hard drive isn't protected in a case, this is not a long term solution. If you want to use a internal hard drive via usb (or firewire) over a extended period of time, purchase a quality external case.
Pros: Sturdy, reliable way of adding practically any hard drive to your Mac
Cons: A bit pricey, but you get what you pay for often. This device, like all USB bridges, are for temporary use only. It would be nice if it had firewire