I would say no.... however... you should take the test. You can take the same test on the online through the kaptest site once you log in. I just dont see how taking a paper test is a good diagnostic. I have to say that the classroom part of the course is complete BS... The instructors rarely know enough to answer detailed questions and the general stuff you can find in books yourself. Also, the online materials is what you are really paying for. They have a total of 10 tests to take online. If you do all the online material, you will do fine on the test. You will have to study a bit on your own of course.
i think you should take it. the more practice the better. Also, taking the diagnostics is required for the higher score grntee so you can get your money back or take the class again for free!