If you are planning to do an intensive course in the US I really would recommend sitting the groundschool exams before you go - this was the best piece of advice I received before doing my PPL. The course is very intense bearing in mind you are learning something very new. I found that once I had completed a days flying the last thing I would have wanted to do is cram for exams. Those people who had to do the exams + flying found it alot more difficult. If the theory is out of the way, you can relax a bit more and enjoy the flying without being exhausted and take time in the evening to think about your flying and prepare yourself for the next day.
I didn't take any formal groundschool for the exams, and was charged £10 for each exam. Like PA28biggles I studied one subject at a time and then sat the exam, and I agree, the confuser is good to work out what area's are likely to come up in the exam. Its probably worth going to your local flying school to see what they can offer & advise - especially in light of the PPL theory changing.
Hope that is of some use & best of luck for your training.
ps I think I completed the exams within a month - studied every spare minute (and worked full-time)!