I see no reason to change the 3B if you are happy with it.
I assume your router is dealing with the PPP side of things, in which case all you should need to do is make sure it has the BT username (bthomehub@btinternet.com) and password (anything as long as it's not blank - I just use 'BT') so you get a PPP session.
If there are any issues and you need tech support then they will want the Homehub connected, but other than that there is no need.
