pashk
In fact I've noticed my accuracy with the official questions is higher than my accuracy with the questions from test making companies.
Good to hear that (about your accuracy), and I agree that official questions are generally much better than test prep questions, although the difference is more pronounced in verbal than in quant. A couple of points:
1. For some questions, a drop in accuracy is not about how well the item was worded. It's actually quite common to see questions that are just badly made (in terms of the logic and concepts used). This can sometimes happen on the GMAT as well, with experimental questions. Questions that make it through testing are normally of very high quality though.
2. I've noticed that higher accuracy on official questions also sometimes results from the fact that test prep companies often prime their students to do well on official practice material, as they use that material itself to design their courses. If you're doing well on brand new questions (like those in a new OG), that's a good thing.