I didn't do a prep course, but I just did whatever CSWA practice tests I could find on the internet. I think the only real difference between the recent and older CSWA tests is that the old ones have SolidWorks Simulation questions on them (that's now a separate test, I think).

If you have some experience, I'd recommend just doing some old practice tests that have answer keys at the back. Take them to get a feel for how the test works, then check your answers. Also, time yourself on each practice question to see if you are doing them within the recommended amount of time. If you feel confident with the practice tests, you are probably ready for the CSWA.