I'm still undecided. I think the perception that Nathan is just another Ben is totally unfair. They've been paired together on the ads so that they don't suffer from the intruder syndrome of nobody caring about Nathan just because he came in late. Similarly with Justynn, he's been sent in there and seemingly told to interact with Tim because Tim and Ben are the two most popular housemates in the game.
In reality, I think Nathan is totally different to Ben. He's a trivia show host, so I think it's fair to say that he's not socially inept in the way that Ben is. I also don't get the impression that he's all about "Aww, look at Nathan doing this" which is what BB has turned Ben into (examples: "Aww, look at Ben learning how to cook" or "Aww, look at Ben learning how to kick a football") due to that ineptitude. Nathan will understand bitchiness, and will probably be a bit bitchy himself. He seems willing to interact with housemates and not just be the typical potplant with the twist of being a bit special (which, in essence, is what Ben is because the housemates have pointed out that he does nothing).
Justynn is trying very, very hard. He seems to have his normal voice and his (over) acting voice. He has potential to be interesting, and that he's willing to shake things up makes him different. It just seems like he's maybe not naturally like that, whereas someone like Tim is naturally a pot stirrer. In a few more days I will probably see it differently though and think he's added some real interest to the house, especially if he creates friction between the bonds that are already there, rather than just between himself and housemates.