Those SAI courses are good. I gave SAI SCJA exam couple of weeks back. I found that version of SCJA little difficult than the mock exams you see around. Those online courses help a lot (especially for SAI SCJA). So go for it. The real exam will have a lot of questions similar to sample exams on those online courses.
Sometimes I find the Sun courses can be a tad expensive. I'd really be interested in knowing your reaction to their course, and if you thought it was properly focussed on the exam objectives, or if it was simply more focussed on getting your money.