Pros
I was able to work in a desired position that I otherwise wouldn't have known was available. I became an employee of the agency on a W-2 basis, which meant they handled the HR functions, payroll, taxes, benefits. The benefits included medical, 401k and training opportunities, though no holiday or PTO. The hourly rate they negotiated was more than I was asking, yet I feel this may have been a factor in the clients' decision to end the contract early. The office staff is responsive to inquiries and communicates proactively. Questions are quickly addressed and the Account Manager periodically checks in to inquire how things are going. Systems and documents are available on-line and easily accessible. I expanded my network of peers while working for the client.
Cons
I met the Account Manager on the day of face-to-face interview and spoke 2-3 times with him after. Not too many issues with the agency, more at the client site. Hourly contractors could not bill for more than 40hours so many were 'voluntarily' working 10-20+ hours overtime unpaid. This culture and precedent made it difficult to set and manage expectations for what could realistically be accomplished in 40 hours. The political and cultural environment at the client site limited direct communication with sponsors and stakeholders, which made information gathering and collaboration ineffective and time-consuming. These limitations also meant functioning in a reactive mode more often than a proactive one. The anticipated 12-18 month contract was ended after 5 months.