Vantaggi
So I'm writing this from the perspective of someone who worked as a BMW contract engineer through In-Tech for 2.5 years. This means that I got paid by In-Tech, but went to work at, and reported to, the BMW assembly plant in Spartanburg, SC. Great work-life balance - I was always able to leave work when I needed to, and any overtime I did have to work got paid back to me as PTO. This is hard to find as a salary-exempt worker. Although, I have heard of other QEs that had much worse work hours (In-Tech claims that they will fight for you if you're work-life balance gets really skewed, but I can neither confirm or deny this). You're really at the mercy of whatever department BMW puts you in. Great Benefits - started at 3 weeks of vacation, and all healthcare is paid for. Depending on the department, the work can be really, really interesting. The BMW culture was pretty easy going, at least in my department. People got fired up about who took the blame for various assembly defects, but no one was mean or disrespectful.
Svantaggi
Salary is extremely low and, because your work benefits BMW and not In-Tech, there is not much room for negotiation. If you value work-life balance over salary, In-Tech is a good fit. Along a similar line, there is no real avenue of promotion with In-Tech. Getting promoted as a contract QE essentially means getting hired onto BMW full-time. Which was very rare while I was there, and is likely to happen even less as BMW is about to stop rolling out new models at this plant for the next few years. As a contractor, you do not have a lot of say for what actually happens at the plant. A handful of times, people pulled the "you don't work for BMW so I don't have to listen to you" card on me. Not a ton of job security. BMW hires contractors so they can cut them relatively painlessly when work drops off. If you're doing a good job, BMW managers will fight to keep you, but a lot of my coworkers were not put in a position where it was possible for them to make a large impact one way or another. If you can't speak German, some roles are difficult to work with. For example, I had to work with German designer's for some components, and my total lack of German knowledge wound up being a pretty big hindrance, since the prints were all in German.
