It's definitely better than stock, it has carbon clutch plates with much beefier preload springs. The factory diff uses a pretty weak "S" spring to preload the clutch packs.
It's not as hardcore as a Torsen, though, which is gear-based; but it's also not $630.
I was planning to use this for my car both on the street as a DD and 1 weekend a month on the road course.