Anti-spam filtering differences with or without Edge Transport servers
If QSS Exchange Anti-Spam Toolkit is configured in the recommended way, from an anti-spam filtering perspective, the only practical difference between a setup with or without Edge Transport servers will be that the the Recipient Filter should not be used without Edge Transport Filters. See Recipient Filter for more information including why it should not be used on Mailbox servers.
The script provided with Exchange does not install the Connection Filtering Agent on Mailbox servers. However, we provide a script which allows the Connection Filtering Agent to be installed on Mailbox servers. See Installing Exchange Anti-Spam Transport Agents for more information.
Apart from the above, we are not aware of any major differences in the functionality of the either the built-in or additional anti-spam agents in an environment with or without Edge Transport servers.
It is very important to test your anti-spam configuration after making changes, regardless of whether Edge Transport servers are used. See Testing Exchange Anti-spam filtering configuration.