Restrict users from browsing directly to VIP.

Absolutely supportable in iRules, but there is more functionality with redirects moving into policy actions in the GUI (or via tmsh) For Hamish's solution, it would look like this:

ltm policy http.redirects {
    controls { forwarding }
    requires { http }
    rules {
        require_fqdn {
            actions {
                0 {
                    forward
                    reset
                }
            }
            conditions {
                0 {
                    http-host
                    host
                    not
                    values { my.domain.com }
                }
            }
            ordinal 1
        }
    }
    strategy all-match
}

Yes, more lines, and doesn't look pretty on the CLI, but multiple redirect rules can be added per policy and managed completely in the system versus requiring coding skills for shops that are leery about coding at the network layer.