There are some things to consider when choosing a material for sighters. The Siman material, the "old" Stren Gold and the Cortland material all have one characteristic that I believe makes them stand out from the other materials: the colored material is opaque. The Amnesia , the "new" Stren Gold and some others are translucent. A translucent material is, in my opinion, much more difficult to see when it is in water.
Further, when using sighters that are not curled, I believe the angler's eye is focused more on the color transition rather than the entire sighter. With the curled sighter, the focus is on the curls and the angler looks for any change here to indicate an interruption in the fly's drift.
Back in the mid-70's, when I began using the colored sections of mono in leaders, we didn't call them sighters: we just called them indicators.
Dave R.