It depends on what you need. Some people find TSFX decent because they don't need a private tutor to listen to them for a whole hour. Plus, having gone to the summer lectures as well, people are VERY comfortable simply going up and asking questions.
As tram said, the notes are extremely comprehensive, allowing students to do more questions which some find to be a better learning tool than having someone sit there and talk to you about theory you probably already understand.
The other benefit is probably the fact that you're basically compelled to do the work whilst sitting in that class...you could do nothing, but that would be the real waste of the "big bucks".
I know plenty of top students who go to TSFX for these reasons...but if you have a lot of difficulty understanding concepts, it's probably better to get a private tutor who will focus on you.