I try not to be a conspiracy theorist, but I heard all kinds of this crap from law professors:
"Don't use commercial outlines"
"don't use old outlines from previous years"
"Don't use commercial briefs"
And then professors started making rules that students couldn't us any outline they didn't prepare themselves either for class preparation or on the exam.
These tricks don't work for everyone, but they worked very well for me. After 1L was over, I decided to take a new approach. I got an old outline (when it was allowed) I followed along in class and made notes on the outline. I never had to read again.
The argument against my style is that I wasn't actually learning the law, and that I was just studying for a final and trying to get a diploma. While that may be true, there is no evidence that briefing every case and making your own outline actually teaches you the law, and it's nearly ridiculous to think that doing that teaches you practical lawyering skills. Law school is so ineffective at teaching actual law, that the massive majority of graduates (even highly ranked graduates) feel compelled to pay a bar-prep company.
I learned to read and analyze cases during my first year, but I learned to do it quickly and effectively by actually writing motions and memoranda at work and for law review. If a property law professor actually wanted you to learn the law, he would bring real-world property-related law suits in and have you write the pleadings and responses.
If you can get good grades using commercial supplements, then you will save a ton of time and that should be encouraged. Instead, these ivy educated super genius professors think that no one in the world should approach law school differently than they did in their super law-geek past.