I think a fair number of law students are anti-supplement. I used a supplement in every single 1L doctrinal class. I found them helpful, except in crim. (As with everything, more than one method works and you should go out and buy them just because I found them useful). I found the E&E series helpful, as it includes questions and answers. With that said, DO NOT STUDY SOMETHING JUST BECAUSE IT'S IN A SUPPLEMENT. The thing that is useful about a supplement is precisely that it covers something your prof already covered in a slightly different way. Your goal is to go back over the material you covered, refresh your memory and make sure you understand the stuff your prof taught. If your prof didn't cover it, do not waste your time with it. If their explanation doesn't help you understand it, forget about the supplement and go to your main materials.
With that said supplements are often very unhelpful in critical areas of the law that will come up on exams. For example in torts the concept of "proximate cause" can be a big issue for exam questions. Supplements aren't going to make this concept clear, because this concept isn't clear. The cases you read will be much better to understand and to use by way of comparison for a "proximate cause" issue.
Again, plenty of students studied differently than I did and did great. Do not follow some wrote guideline if it doesn't feel like it's working for you.
AND DO NOT STRESS OUT ABOUT EXAMS YET. YOU HAVE A LONG WAY TO GO.
1: Criminal law as Professor Buell teaches it is mainly statutory interpretation. Cases, and policy analysis are relevant, but only provide guidelines to aid in interpreting and understanding criminal statutes. Consequently, I thought supplemental materials were essentially useless for that class.