Pros
Because UC Merced is a new school and the grad student population is small there are many opportunities here that would not be available at other schools. In the sciences it is highly likely that you will have the chance to learn multiple techniques and become familiar with many instruments rather than being stuck as the "super user" for one instrument. Additionally, it is easy to talk with senior faculty to get their advice or to learn from them because there are so few students they can spend time with almost anyone.
Cons
The small size is both an advantage and a disadvantage. The disadvantage comes in the form of not always having the infrastructure that would be available at an established school. Another drawback that comes with being the new kid on the block is not having an established reputation. However, these drawbacks are not life or future career ending and the Pros, in my opinion, outweigh the Cons.