I am a 1L, and thus far briefing has really helped me. I was called on in class last week, and everybody came up to me afterwards and asked me how I prepped. My response was, "I had a really good brief." It was only 1 page, but I somehow got lucky and everything the Prof. refered to was on there.
I also tailor my brief to fit the prof. For example, my torts Prof. is really big on policy, my property prof. always wants to hear each sides argument and point by point what the court did in response. So I have a different brief template for each class.
As of yet I have not bought canned briefs. I have looked at them in the bookstore and may purchase them later.