A multi-tenant firewall for an MSSP

Hello All, We are planning to implement a multi-tenant FW/UTM and start providing security as a service, I would like to hear if anybody had experience on this, and if there are any recommendations for the UTM's vendor. People/customers here are more familiar with the Fortigate, however, we need to build a well-rounded solution that suits wide range of enterprises' business needs. Thanks, Ramy