Pluspunten
They do make an effort to place you in a good fit with the on site company.
Minpunten
If you care about work/life balance, look somewhere else. The difficulty of negotiating maternity leave was a headache. They only want you to be gone for the bare minimum of medical needs and do not encourage longer leave for bonding purposes, which FMLA allows for IF the employer agrees.
I, and others at my site, have had many problems with PTFS living up to verbal promises. They do not keep up a relationship with you, so why would they fight for you as long as they have a body in the position?
I have stayed because my on site company has been great.