The distinguishing feature of the General GRE is the weird format of the questions in both the verbal and math sections. The questions are not straightforward as they are on the SAT and ACT, while the material itself, e.g. vocabulary in verbal, algebra/geometry/probability/data analysis in math, are not advanced. I would suggest that you get a practice book with practice tests on CDs to review the material and learn the format of the questions. Many of the questions look harder than they are due to the weird format. You can get familiar with the several types of questions. You can do well on the test by practicing a lot. I am not sure about the class. Those classes always cost a lot, and I am not sure what one gets out of them that one can't get from practicing by self.
When you go take the test, you sit in a cubicle with a computer. Sensory wise, the cubicle is quite isolated, and you can't see anyone from it. There are noise-blocking headphones for each cubicle, but they are rather uncomfortable to wear. I wore them for most of the test, with my ears hurting, but they blocked out most of the noise, eggspecially the other test takers typing. You can request disability accommodations, perhaps to take the test in a separate room, I am not sure. The test center is like Fort Knox, and you can't take anything eggsept pencils inside. I wanted to wear my hat to block out the fluorescent lights, but that was not allowed, because the video cameras tape you from the ceiling. Disability accommodations need to be requested for that.
I did not spend much time studying for the test. I spent a lot more time on the GRE subject test. I spent about a week practicing the test, and I did well. You can kind of tell how much time you need to study if you first review the math, then take a full practice test, and see what scores you get.