I think Niger Triggers get more attractive with age for sure......I will say this about Trigger Compatibility, NO Triiger (that's 0, none, nada) are always compatible. Niger for me are the best example of the bigger and older they get, the nastier they get. I have kept 2 Niger's for 5 + years (different tanks), a 2 inch Niger is a very different fish from a 5+ inch Niger. My Pinktail and Niger were in a nasty fight when they first got together, both got beat up pretty good, but they have settled things out and get along fine now.
I will get some disagreement on this one, but I have now kept 4 different Huma Triggers (Rectangle and Picasso), they are easily the LEAST aggressive Triggers I've kept. Huma's I've kept are only concerned with one thing, food.