What's the difference between an immigration company and an immigration bureau?

To put it bluntly, immigration companies are intermediaries. If they are agents handling immigration business, they will charge a lot of agency fees. In other words, if you give them a copy of your materials, they will polish it for you and give it to the corresponding immigration office. As for whether to approve or not, it is beyond their control.

Immigration is an official institution. They are responsible for approving immigration affairs. They are responsible for listening to the materials submitted by individuals or companies, selecting applicants and finally determining the accepted candidates.