A 'different' Justin? This is a very different Justin than the one we saw at the end of S1. And in fact, he's very different from canon!Justin throughout the series. His characterization still rings true to me, but it's been reshaped by a different life. Would you explain these differences solely by the absence of Brian in Justin's life? Or is there more going on here?
I would say that while Justin's life has changed, that this is exactly what I did in Pulse Point: Taken pieces of canon!Justin and integrated them in a different way. I don't see him as being progressed/aged/changed as he is in, say, "A Matter of Time," where IMO his voice, attitudes, his actual personality are really very different, presumably due to his life in the fast lane in Hollywood.
He feels, talks, walks, fucks, and "reads" very much like a mixture of S2 Justin with S5 Justin, a mosaic of a Justin who has had to learn a hard lesson and perhaps learned it too well (S2) and a Justin who has become thoughtful and started to make reasoned choices about how to have the life he wants (S5). It's true that the integration of both those things in one moment in time is not something we saw in canon, but in its parts, it's made up of canon!Justin.