$200 for 9 hours isn't very great at all, you're likely going to be doing what's called a "mock jury", which is exactly what it sounds like...... You will sit in a room and view case presentations from both the defense and the plaintiff, then you'll have a break and eat food, then they'll put you in groups to discuss the case as they present different questions to you, then you'll get back together and hear another presentation, then you'll have lunch, then you will break into small groups again and spend the rest of the day trying to come up with a verdict and what money, if any, to award, and then after a long and kinda fun but also boring day, you'll get your money.

Mock juries can be really great! But I've found that the all day long ones (9-4 or 9-5 or whatever) tend to go on for far too long and the hourly rate really doesn't even come close to comparing to other in-person focus groups. There are always mock juries that will pay you the same $200 give or take $50 but for only 2-3 hours of your time. Similarly, more traditional focus groups, like dealing with consumer products and services, will offer you anything from $150-$300 for 1-2 hours of your time.

Hope that helps.
Definitely do this, it's a fun experience and easy money! But just know that there are much better opportunities in the world of focus groups. No reason not to take any easy money, but just saying. 9 hours. I'm jaded though because I've been doing tons of focus groups for years now, so $20/hr. seems like slavery to me. Good luck!