I found the feedback activity to have the following limitation when using as a 'contact us' form:
1. It is meant to be submitted once. Even if it is configured to allow multiple submissions, previous submissions get overridden. A contact us form on the other hand should allow users to submit as many queries as they like with all queries recorded in the back-end office.
2. It could be me not being able to figure it out but a feedback activity on the site homepage with guest permission allowed still requires the guest to login when the feedback activity link is clicked. I have the below capabilities granted:
- mod/feedback:complete
- mod/feedback:receivemail
- mod/feedback:view
Perhaps it would be worthwhile exploring the help desk plugin.