RE: BGP advertise-best-external on RR

If your network is such that only a handful of routers supply redundant paths, then you can set up iBGP sessions with those directly without going via route reflectors. You can have most routes going through reflectors and a few through direct BGP sessions. Not everything needs to go through route reflectors. You can even do both: Have a router peer with a reflector as well as directly if you only need the redundant routes in a few places. You will end up with duplicate routes, but that's not a show stopper. You can avoid duplicate routes with route maps. You can have multiple route reflectors with different cluster IDs that carry the redundant routes only. Clients can peer with multiple clusters. Use route maps to avoid duplicate routes. These last things get complicated to manage, so I'd still go for add-path if at all possible.