I use public IP on PPPoE just fine. I do not use the user manager to assign, I just use a pool. User manager is just to allow access. It is just like with private, however, it seemed to run faster/ better when I routed a subnet to the MT running PPPoE, rather than letting it respond to broadcast. Also when I added OSPF to the network, each pppoe client IP was being distributed, which may be usefull for some redundancy planning.