I have never shot in low light, so I cannot comment on their usefulness in low light. What I do like about night sights is the ability to find my handgun in the middle of the night. When I see the three dots glowing on the nightstand, I feel like I can grab it easier than if it wasn't glowing. Now that I see some of the other posts, this seems like a pricey way to locate the gun. I never looked at it that way. Now I wonder if I should just buy some great target sights (at least on one of my GLOCKs) so that I can be more accurate for about the same price or less. Or perhaps spend the money on a light, laser, or light/laser combo.
I have Ameriglo night sights on my GLOCKs and they are bright enough in low light to line up and really bright in the dark. I was thinking that if when I get my FNP-9 and decide whether or not I need night sights, I will go for the Ameriglo night sights on it.
They are cool though, perhaps getting them with the gun, being cheaper, is the way to go.