Dave,
Not sure what your wrist size is but my experience with the eBay rubber was I found the rubber didn't curve as smooth as the gen rubber. Specifically the area in between the lugs. The ebay rubber doesn't taper like the gen. This may not be the case for guys with a 7"+ wrist but with my 6.75" wrist the gen made a difference. I went gen and if you ask me I could never go back to the rep.
On a 42mm case the "curve" difference was mild, but there. On a 45mm case the difference was huge.
The mrsp on the gen rubber is up an around $200.00. However, I've went through 2 or 3 now and I've been able to buy the gen rubber in between $100.00-$150.00cdn on eBay and WUS.