you can be sure that the real exam is going to have passages that are more than 4 sentences long and aren't going to have 6 questions in a row asking about the same concept.
This is the most important point in this thread.
The Gold Standard exams serve a very particular purpose and for certain kinds of students they're a great resource. But they absolutely are not a "first line" resource that you should go to right away.
I always tell students: Gold Standard is good for skill-building, not simulation.
If your goal is to simulate test day and generate a realistic feel for the actual exam (and get a representative score), then you only have one choice: AAMC practice tests. That's it.
There is no close second.
As has been said, the Gold Standard tests tend to be more nit-picky, more "science-y", and will ask you very similar questions multiple times in a row. That's not realistic when it comes to simulating the exam. What it is good for, however, is skill-building.
The real MCAT would never ask you to solve for pKa or Ka on four questions in a row, but the GS tests can. However, solving for pKa is a skill you need to have for Test Day. So asking you to do it four times in a row is a good way to build up that skill.
So wat do?!
I'd suggest this: if you're looking for full practice tests to take on a once-or-twice-a-week basis to simulate test day, you should do this: 1. AAMC, 2. Whatever tests came with whatever other prep you're doing (KTP/TPR usually include online practice tests if you buy their books, etc.), 3. TBR
If you've already gone through your MCAT books, you have a schedule laid out for taking your AAMC's and what you're looking for is just some 70min timed section practice that's really technical to do every day, that's where the GS tests can serve as a great resource. Again, they're not your "first line" prep materials, but if you've burned through other stuff they can fill that gap nicely.
Full Disclosure: I do not have any professional relationship with GS at all. No referral relationship, anything. I personally recommend GS to something like 10-15% of our own students.