this is what I found from a blog which answers my q. I thought it would be worthwhile to know:
https://madgmatter.blocked/ :
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GMATPrep: Must do. If you want to do well on the GMAT, do well on this. This is the most accurate representation of the actual GMAT. The SC level is a notch higher than on the actual GMAT, but everything else is pretty similar. The math part may seem a little tough, but that’s the kind of questions that come on test day. But to tell you the truth, the software is very crappy. Firstly, you can’t review your AWA responses from the test. Then, your score is flashed only once, after you finish the test. Once you click 'OK' on the screen with the score, you can't retrieve it again. Also, there are no explanations for the test questions. But there are a few questions in the section test with explanations, so be sure to do those. One more thing, I found the font used hard to read, but get used to it, because this is exactly the same screen you will be getting on test day.
PowerPrep: This is GMATPrep's predecessor. This is not officially available, so you will have to download off some site (When I last checked, this one was working -
https://www.gorillatestprep.com/gmat_resources.html) . It’s a little easier than GMATPrep, and a good confidence booster J. The best part about this software is that it gives explanation for every question.
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