Definitely one of the best math professors here who explains things really clearly. His lectures are very well structured with 5 minutes of review + new materials + 1 minute of preview of the next lecture. I have never been to his office hours (mostly because he really did explain things well so I've got nothing to ask lol) but I assume he would offer some help for homework. Homework assignments are mostly 4-5 problems written by the professor himself. After the due time, he would post very well-written (LaTex!) solutions on CCLE. Tests are not hard but a little computationally heavy.

If you're conflicted about who to take for this class, definitely take Tong. I didn't realize how great he was until I started taking 151B with someone else. I wish I could have him again.

Tong likes to review the previous class for the first 10 minutes of lecture, which makes new material a bit fast paced, but is helpful if you missed a class or tend to show up 5 minutes late.
I got pretty wrecked by the first midterm because i studied a lot of the theory and didn't work on practice problems enough. His tests are very computational, so studying with practice problems is the way to go. I applied this for the second midterm and killed it, which worked out well because it replaced my first midterm.

(P.S. please learn to pronounce the Greek letter "xi")

After taking class with him I recommended Tong to all my math major friends... He is by far the clearest and one of the most helpful math professor I've ever had. Some of his homework problems are thought-provoking and helps you heuristically understand the materials, instead of just memorizing the formulas and apply them, and during office hours, he is very willing to discuss the homework problems with you. Well, his tests are not conceptually hard (like you won't stare at the problem for minutes and don't know where to start), but they are a bit long and computationally heavy. But I mean Math 151A is a computation-based course so it's fair to expect a lot of computations on the tests...
Overall, if Tong by chance teaches this class again, take him without hesitation. Really really responsible and great professor.

Very helpful professor. Wonderful lectures. Homework is medium-difficulty if you go to Office Hours. Hard without. So go to office hours!!

Midterms and final are similar to homework difficulty but are very computationally heavy. Many of the problems consist of taking the doing the algorithm mentioned in class but within an hour (for midterms) or 3 (for finals) so make sure to be fast with computing.