If you have several companies using RushFiles, you can easily share the different shares with your main user.
What you need to do:
You will need to share the data shares from your companies with the main user*
You can follow this guide Share files and folders with others
When you share the data share from the companies you are attached to, they will show in the web-client, PC, Mac and mobile devices so you can access all shares with the trouble of loggin out and in with another user.
* Main user is the user you prefer to use and login with