Pros
It is slightly better than indentured servitude. If you work for long enough you may be promoted to full time and recieve some benefits.
Cons
Flex pool - you will have work while there are projects for you, if there arent projects for you, you get to sit at home and collect un-employment until another project comes in. You will probably be spending half of your employment here collecting unemployment and waiting for contracts to come in. Management treats the employees poorly and tend to lead people on with promises of promotions. You may get laid off the same week your boss drives a brand new corvette to work, then they will re-hire you for a lot less than you were making before. No on-site HR, and you will be lucky if anyone actually knows who to talk to if they forget to pay you. There are a lot of problems with people getting paid on-time or sometimes even at all. There have been many cases where people were sent home for extended amounts of time (a month or more) then called back in to work, and when payday comes they find that they are "no longer in the system" and cannot collect un-employment or get their paycheck till the are "put back in the system". You will probably wind up working as a test lead at some point but not actually getting a pay increase, though you will have all the responsibilities of this. This could go on for as long as 3 years with no raises or compensation.