Ventajas
Hopefully you just have to deal with the company they contract with and not them. In our case my cohort had to deal with them months before and into our assignment due to their constant mistakes.
Desventajas
I worked as a contractor for another company facilitated by Joule (System One). No one in the entire company cc's each other in emails and you have to constantly restate yourself to explain the problems they continuously cause. They constantly lose documents, blamed my coworkers and I for the deadlines they missed, and are extremely late to respond to emails, text, or calls. We had our positions threatened because they claimed we missed deadlines, but they either never shared required documents or deadlines, or the deadlines were met far in advance, but their staff lost the information, even if it was sent digitally. I have never worked with a corporation so barely able to fulfill their basic functions. I had to function as an HR employee in addition to my actual job just to make up for their complete apathy towards their employees.