i went to the chem and physics lectures every holidays (cos my school teachers were a waste of space)
they were good for me... I also did some 3unit maths, they were crap crap crap... cos its just impossible to teach maths in that lecture format with people at all different levels, and they can show the most extreme hard examples and ya just feel discouraged...
the english ones i went to were awesome as well, specially the Transformations and Telling the Truth and Journeys, actually they were all excellant.
WAIT... on the maths thing, the study guides for maths are brilliant... so spend your money on them and not the lectures
hope that helps