Pros
There aren't any pros, really.
Cons
At the job I worked we were the least paid. People constantly quit to work for the other contractors who paid easily $5 an hour more. We were also the only contractor that had to have a half hour unpaid lunch in the middle of a 12 hour shift in the middle of nowhere. There was a lawsuit over it and Battelle lost. Also, when I had an accident on site, they rushed to throw me under the bus and really pushed at the boundaries of what was legal. They expected me to come in with an unsecured break while on heavy drugs and sit for 12.5 hours and NOT sleep while on the medication designed to make me sleep. As long as nothing goes wrong, it was an okay job, but if something goes wrong they will sacrifice you in a second.