I have had both. I replaced the Spec for the MBP with a Techshell. The Techshell fits much better and unlike the Spec allows the MBP to open fully, the Spec does not. I also have a Spec on a MB, but on this unit the case fits much better.
As far as scratching goes I have the Spec on both comupters for months now without any noticeable damage. I have also found that I avoid dents and dings that I have recieved before on my ibooks and powerbook.
So in sum it does what it is designed to do, and serves as nice appearance boost as well. But then again, I wish I could spare the 400 or to get a Colorware custom case. They do sweet work.