Allow based on IP for uri starts_with

What you've got should do a good job.

My only suggestion would be to create a Data Group (iRules -> Data Group List -> Create (Group of Addresses)) that you could add additional qualifying IP Addresses to without having to add any to the actual iRule.

when HTTP_REQUEST {
if { ([HTTP::uri] starts_with "/admin") and ([matchclass [IP::remote_addr] equals $$IPAddressDataGroup]) } {
HTTP::redirect "https://foo.com/admin/index/index/"
}
else {
HTTP::redirect "https://foo.com/login/index/login/"
}
}