Contrary to popular belief, chromis are not nice fish (especially to each other).
Flashing may happen without the female but the duration of the color display will not be as long or pronounced. It may do it as a form of agression towards other fish.
Both have the potential to be absolute terrors but more people have 6 lines that they love and swear are model citizens over the YT. I don;t think I have ever heard anyone say they love their YT damsel .
You will have a harder time locating a 4 line and you may find it to be a little less agreesive that a 6 but this is a fish-by-fish thing.
Contrary to popular belief, chromis are not nice fish (especially to each other).
Flashing may happen without the female but the duration of the color display will not be as long or pronounced. It may do it as a form of agression towards other fish.
Being he was only going with 1 damsel, I think the chromis makes a better choice, but yeah some chromis are solitary others shoal together. Being none of his other fish choices resemble another chromis I think one would be a pretty safe bet vs getting a damsel.
You are correct. A lot of people get sucked into buying a group and get left with only one. Depending on the fish, you can still get a little #$%&@ though !