Pros
There are almost no pros of working with them. They will bother you constantly with requirements and unnecessary training courses during your personal time.
Kontras
They will get to keep most of the money they charge their clients. For instance, they will charge a client almost 2500 USD for you and pay you 400 USD and demand ridiculous working condition. Also, they will apply ridiculous penalties and discount money from you so your compensations will always be decreased and they will get extra profit from you. It it needed to be remarked that several clauses in the contract are illegal in the US where they are based as a company and that they will apply the contract unilaterally, In my personal case, they have decided they will keep my final compensation for themselves stealing that money both from the client and me. I strongly advise you to use them temporarily and leave to a serious place. Or don't work for them at all.