There is actually no overlap between the GMAT paper tests(all 9 of them) and the GMAT prep software. Although. there is overlap between GMAT paper tests and Official Guide 12th
/13th Edition. The questions in GMAT paper tests are on average easier relative to GMATPrep software, partly because one has less time per question. I wouldn't recommend paying for those tests, but I would still recommend you to practice with them, especially if you are having trouble with easier/medium concepts.
Free Video Explanations: OFFICIAL GUIDE FOR GMAT REVIEW 2015.