In my experience, Tusq is brighter than bone. YMMV.
Archtop bridges are entirely different animals. They are floating, not glued, and very few have a bone insert on top.
Usually, archtops have a more focused sound, good for solo or comping work, with little sustain to muddy up single notes runs.
In comparison, flatops sustain forever, more so with Tusq or bone, way less with ebony, rosewood or any wood saddle.