Pros
MARCOMM has been in this business a long time and they understand my dedication site very well, so I never doubt that they'll give me good counsel with any issue or question I have. MARCOMM also understands that in order to recruit skilled and effective professionals, they need to offer salary and benefits that compete with traditional full-time employment. In some respects, my employment benefits improved when I started working for MARCOMM. Lastly, MARCOMM worked with me and my dedication site when I asked to take a few months off to travel abroad. They care about meeting the needs and wishes of both the dedication site and their employees, and they're happy to look for creative ways to do so.
Cons
One potential con is that MARCOMM is fairly hands-off once an employee is settled at their dedication site. I think this is partly because MARCOMM hires experienced professionals who don't need a lot of oversight. It may also be due to the distance that some dedication sites impose on agencies that supply contract workers. For example, my dedication site uses a third party to act as the liaison between hiring managers/supervisors and all contract agencies.