Pros
If you are desperate to work, this company will contract you quickly and probably without telling you first what you are signing up for, which will make you feel bottomed out and invisible. You may get placed in a good company-but it will be tough to work alongside the privileged direct hires while you are doing all the work and watching them coast, enjoying their time off, 401K/etc, and getting their hefty bonuses on your back. It is possible, not probable that you may get direct-hired, but you will work harder than ever for that crumb of hope and will get strung along for as long as possible. Work is work in lousy times...
Cons
No time off, no real benefits, just a payroll company that provides work for the desperate and cheap disposable professional/educated labor for big-name companies