I have compared them to Specturm Noir (as that's what I have) but not Copics. I actually have a review up if you're interested:
Product Review: Stampin? Up Blendabilities Markers (with lots of samples) | Stamping | CraftGossip.com
The main things I liked where the tips are really nice (better then Spectrum Noir), having three shades in the same color made them really easy to blend (not guessing what colors work together or maybe not having them), the colors are rich and deep and they do gradiate (sp?) really nicely.
Blendabilities
