Most Magnet classes are difficult. They are much more difficult than "regular"/"non-magnet" high school courses but are weighted the same as them. There are, of course, classes like ECAD, with their, um, rather unique curriculum and reputation.
Teachers at the magnet have a reputation for being bad ass. They make their class difficult, but in style.
Overall, the whole magnet experience is enjoyable. It is the place to go in Laredo for the best academic program with plenty of fun in it.
Student: I'm the United High School valedictorian. I have a GPA of 106 out of 100.
Anyone Else: What was your SAT score?
Student: An 1850 on the 2400 scale.
Anyone Else: Oh, you must be non-magnet. See, magnet students have harder classes and, thus, lower GPAs but way higher SAT/ACT/AP scores than you.