Pros
They provide great support for new staff coming from overseas. They assist with setting up your new life in Japan by finding a place to live, assisting with registering at the city hall, setting up your local phone contract, and any initial shopping for your new apartment.
They will continue to support your if you need assistance with language boundaries.
Cons
Changing to full-time is tough. As a contract worker there are no bonuses, so not much incentive to improve quality of work. There is only a resign bonus.