I would recommend self study with the text book in which you are comfortable with. ISCA needs repetetive reading and memorizing the key points. So, even if you are attending classes for 120 hours on listening to a lecture, you need to prepare on your own. Have to allocate more time on reading on own and remembering key points.
Hence, I would recommend, invest on a good book and time for preparing for ISCA. techniques like, taking short notes, writing down the answers that you learned, revision will have more impact on gaining mark.
If you are not comfortable with reading for the first time, and hearing goes to the head faster than reading, then you can opt to classes, its worth it. (I dont know about the auther/ faculty you have mentioned)
If you love to read, then self study if preferable.
Its my general opinion.