I have one Radian safety and a handful of FCD's, if that tells you anything. They feel snappier and "sturdier" I guess. All of mine are the quick levers, which I really like. I have no issues with the Radian, though, so I won't be going out of my way to replace it with an FCD.
The Radian is also known to have issues with Geissele triggers, if that matters. I don't have a Geissele in the rifle with the Radian, so I can't speak personally on that.