Yes, I have done them and I do agree that they are a bit tougher, but if you read the questions with patience and practise them more I am sure you will feel more confident to answer. Its natural that as a human being we get perturbed when we confront unknown/unseen problems, but as we get more of them we get used to them. The key is to do the
GMATPrep as many times you can, before you face the real one. It has a lot of hard/hidden questions which will pop up only when you do better. As the old saying goes "GMATPrep is the closet relative to real GMAT" So tame it baby. Date it as much as you can.