A couple of points about Barbri. First, Barbri is a national company and they provide state-specific materials for state bar exams. I will use Texas as the example in this post, but if you don't care about Texas, just supply the state you do care about.
Second, Barbri is probably the largest and most used bar preparation couse on law school campuses nationwide. There are others, but in the end, most law students go with Barbri. As a One-L there will be Barbri representatives around your campus. You can sign up for Barbri your first year and "lock in" the price for the entire course when you need it after you graduate. I believe the cost for signing up is between $75 and $150 your first year. If you do this, you "lock in" the current price that Barbri is charging the 3Ls on your campus that year. In other words, for an initial payment, the price you will eventually be charged in three years will be the same for the year you "locked in." Some law students who don't make up their minds to go with Barbri until their third year and then end up signing up for Barbri as 3Ls have to pay sometimes as much as $250 more than their peers who "locked in" their first year. You see, the cost for the Barbri bar prep course keeps increasing, usually by about $125 a year. I believe the cost for the entire course is now over $2,200.00. When you "lock in" your price your first year, you also get a Barbri First Year review book full of first year topic outlines (contracts, torts, federal civil procedure, criminal law, property). The outlines are good, but they are really geared for the bar exam. For law school purposes, they help you to organize the notes you have taken from your professor when you do your own outlines but they cannot be used by themselves to study for your law school exams.
The material tested on the bar exam is different than what you learn in law school. This fact surprises most people: the most important part of the Texas bar exam (or really almost any state bar exam) does not test on Texas or state-specific law. The most important part of the bar exam in almost all states is the Multistate Bar Exam ("MBE")--a 200 question multiple choice exam brought to you by the National Conference of Bar Examiners. This test tests on "majority rules" and "minority rules." A majority rule is a rule of law that applies in most states of the country. A minority rule means a rule a few states, but not most, apply. The MBE also tests on the FEDERAL rules of Evidence. If you are trying a case in a Texas state court, you would use the TEXAS Rules of Evidence. The MBE only tests on the FEDERAL rules of Evidence. So, the Barbri outlines do you give a sense of the structure of a topic, but if your law school professor emphasizes the rules of law in the state where the law school is located, the rule shown in the Barbri outline may not necessarily be the state specific rule. The bar exam may have a question where the right answer for the MBE would be the wrong answer if you were applying Texas law.
In your second year of law school, Barbri also gives you as part of "locking in" your price your first year, a second year state-specific outline book. This book contains state-specific outlines for upper division topics such as Wills, and state Civil Procedure. These books are slightlly more helpful for studying in law school, but I would still suggest doing one's own outlines and using the Barbri outlines more as a guide for which subtopics fall under more general topics. All this being said, Barbri is just about essential for most people in law school and for those studying for the bar exam.