Feline Pheromone - need some recommendations

I know I've heard discussions here about using a feline pheromone to
help ease the entrance of a new cat in a household with existing cats.
A friend just adopted a 4 yr old male cat and his older female is having
troubles adjusting. I think he's doing everything right - keeping the new
guy (Rusty Joe) in his own room with a childrens gate to separate physically
but still allow the two to smell and see each other.

Would a pheromone spray help? If so, which?

Thanks
Tam