They implement Double NAT-ing to solve the problem. They make the required changes at their end and walk you through the changes to be made in your
router. With that you pretty much get a static WAN IP.
Client router end changes:
PPPoE settings will be changed to static ip. No portal login required.
They provide you their
DNS settings that you can discard, if you want to use
Google or other 3rd party DNS.
You may not require DDNS going forward. But if you still need it, you can directly assign your public IP to the DDNS. If you still want the router to register, then your router should be capable of registering 'NATed Public IP' with your DDNS provider.
As expected, ping slows down considerably.