For me the answer is no. It is never good. Most of the time in my previous, ie before married life, if I met up with an ex we would end up getting into midnight dates that always took place in the bedroom. As I have grown I have learned that for me seeing and ex after the fact is not a good thing.
One of my good friends is dating a great guy and out of the blue his ex shows up ... hmmmm. What does she want?? She apparently wants to meet up with him for dinner to "catch up". So does the great boyfriend meet up with his ex or not? What do you say as a new girlfriend? You can't tell him no but you can certainly tell him about your feelings. I guess this is a good test of the relationship but why do you need to test it?
I hope he makes a good decision .. like meet her at McDonald's at 8am in the morning or tell his ex no and buy his new lady friend some beautiful roses.