The GS tests scared me for a bit! After doing content review for a good month and a half I started doing practice tests every other day which I will do until my sitting which is this Friday. I did the 10 GS tests before starting the aamc's so definitely have a few thoughts on them.
I actually thought they were relatively easy until GS 7. The physical sciences is brutal on 7-10 and in my opinion not very reflective of aamc. The degree of knowledge and the complexity of the questions were quite a bit more difficult in PS and very calculation heavy. GS also just has alot of terribly worded and multiple-answer questions. That being said, I think they prepared me to be efficient with calculations which is very important if you get a calculation-heavy exam. I felt the aamc's were much easier in PS so it was a nice transition going from GS to aamc. My average is 3 points higher on aamc.
Verbal is odd. I don't think it is quite as bad as everyone says but there are some questions and answer choices that make absolutely no sense. The scale they use is wild and they give you a much higher score than you actually make. Regardless, it has practice value so I would still recommend using it just don't give the scores they give you too much credit. My average aamc score is actually a point lower in verbal despite being easier and getting more questions right in aamc.
Biology is a bit different than aamc but I feel like they are pretty similar in terms of difficulty. GS bio is much more info based than passage based like aamc. Once again, they throw a crazy curve on bio and make you feel better than you should. My aamc average was a point less than GS.
Overall, Ide say they're were buying and using considering the price but I would definitely do them before doing the aamc's and not taking your scores too seriously. I hope this of some help!
