I would not recommend Prof. Fronsdal. The two main problems are 1) the material and 2) communicating with him.

1) In 105B, he did cover what most 105B classes generally would cover: Hamiltonian mechanics, collisions and Conservation of Momentum, gravitation and Kepler's Laws, scattering theory, special relativity, 4-vectors. However, in about 3, 4 weeks in, he introduces group theory (from Math 110A) and attempts to review some concepts from linear algebra (while bungling up various definitions) and differential geometry (generators of infinitesimal translations, rotations, etc.). The class takes a turn for the worse from that point on. If you want to cover topics sufficiently for usage in other classes (such as scattering theory for Physics 126), then you're stuck resorting to the not-so-great textbook that Fronsdal only refers to once a week (Marion and Thornton, Classical Mechanics).

2) Communicating with him is a problem. He wears a hearing aid, and I know it can't be helped, but . I attended his office hours almost weekly for homework questions. He will answer nearly anything you throw at him, but you'll find yourself raising your voice to the point where the rest of the faculty in the PAB 4th floor theory cluster will hear you. This is even worse in class when people attempt to ask him questions, and it may take as many as 2, 3 minutes to get the whole question across before he starts to address it.

In the past several quarters that he's taught this class (the 105AB sequence), I feel like the students were lucky enough to have decent/good TAs who knew their material well or would invest their own time to consult Fronsdal on any mix-ups or anything simply not understood, and relay the message back to the students. He has a very generous grading curve, but don't let that fool you into thinking you'll get that much out of the class otherwise.