Pros
Being a contract worker gives you the illusion of having a great job--the assignment itself working at GM, Fiat, or Ford is first class. Make no mistake, you will be given the same level of responsibility as regular direct employees. The Bartech folks are pretty supportive and are pleasant enough to deal with on the phone. There's only one reason for being contract--the opportunity to get a foot in the door and be hired direct. You are a W2 employee and not an independent contractor.
Cons
Lousy medical and dental benefits. Your coverage begins after the first month of full employment, so if you start on Jan 1st for example, you don't qualify for benefits until March 1st. And it costs you an arm and a leg. You get only 5 days of vacation per year, and if you get sick, there is no paid sick leave. There are no promotions and you do not accrue any years of service. Though the OEM's (to their credit) treat you about the same as any other employee, you are effectively a second class citizen--you do the same work (or are working harder to prove your worth) for less. The entity who really profits is Bartech, for basically doing (in my opinion) very little. It's difficult to stay motivated; that's why there's so much turnover in contract staff.