The thing is that it depends on the topology. An example, I have a slave site where all BHS reside, but I have some clients that are nearby and the only viable solution is to connect them through the slave site, thus the client being a master site faces the tagging problem.
For now I am using a switch for tagging purposes, but sometime its not practical to install a switch for only one small customer.
This is where, I believe that it is best to have tagging on both master and slave radio, as PTP450 does.