That period when it's no longer light but not quite dark will be when any sight is not at it's best.
It needs to be pretty dark for Tritium, and there still needs to be some decent light for the fiber optics to "glow".
One thing about TFOs is that they will stand out and be easier to see on overcast days, in general all daylight conditions, when Tritium only sights are at their best in the dark.
All of these, whether TFOs or tritium only have the front sight much brighter than the rear dots, so you can concentrate on the front.
As someone else said, the TFOs are nearly half the price of the Trijicon sets, so I can afford to have them on every one of my handguns.