I've taken all five tests.

My advice is: if you have plenty of time on your hand, and have exhaused all the material provided by the testmakers, they might be worth taking.

The math tests cover a wide range of topics and give you a fair idea which areas you need to work on. The verbal tests were okay, although the last verbal test was deceptively easy.

My Quant scores on GMATPrep were much higher than my 800score Quant scores. My verbal scores on both GMAT Prep and 800score exams were within the same range.

Hope this helps.

I kept scoring between 35 and 40 on the Q part. 50 on the real thing. Didn't bother with V.

Thanks......