I have to disagree. I thought the books are best used throughout 2nd year, and they are best if used in a group format. If you are able to get together with 3-4 classmates and discuss each case in the UCV, you are really able to learn a lot just through the discussion with your classmates. The books might not emphasize basic concepts, but if you are able to correlate clinical findings to basic concepts that you get from your classes, you end up reinforcing both and getting to a whole new level of understanding.
I do agree that if you are crunched for time that UCVs might not be the most efficient way to review for Step1. But if you are using them throughout the year with your classes, they are excellent. Certain books are solid(path, micro, biochem) and certain ones aren't the best (behav. sci, pharm). PM me if you want any specific opinions.