I know someone who used them. He said it was basically a crammer - you went over each subject in a day, and then sat the exam before you could forget it all. He passed, as did others, but he said there were lots of gaps in his knowledge...not surprisingly, perhaps. He didn't sound as though he either recommended them or the opposite; I got the impression they were good for what they were designed to be - a crammer that enabled you to pass the exams, even if you didn't have much real knowledge at the end.
But bear in mind that's second-hand, ie, my interpretation of what someone else thought!