this is what I have learned about the 800 score tests. They are really not adaptive. They would throw the same 37 questions at you no matter you get a previous right or worng. Depending upon which ones you get right, the software calculates your score which is not the way actually CAT works.
800score may provide some good quant questions to pratice but avoid them as tests and also avoid the verbal.

I would agree on not using the 800score.com and Arco tests.

I got the following tests from my friend..Ever heard of these?

• Crack GMAT Diagnostic Test

• C.A.T Prep's GMAT simulator

Can someone tell me if these tests are worth taking? I have only 1 test of kaplan and 2 tests of old PowerPrep left. Can you suggest any other good tests that are available? I have already taken Princeton Review and GMATPrep..

I also want to know if the 20 GMAT sets are good for practice and if the difficulty level is same as in GMAT..

I ran across some posts about Crack GMAT tests in another forum, and people said to stay away. I have never heard of the other ones you mentioned. In general, I would stick with the well-established companies you hear about most often in these forums. If necessary, you can uninstall and reinstall the software to retake tests, and get mostly new questions. I'd do that before taking unknown tests.