Everyone is enamored with real shell. Let's face it. It is sweet to strop on. Soft and supple. Nice draw!
It's also somewhat rare and expensive.
Then we get to actual effectiveness. Some others are stiffer, coarser, slicker.
As far as effectiveness goes, bridle, pigskin, horsehide, boarhide, even cowhide are every bit as effective in quality hides, IMO.
Rezdog mentions zippy secondarys.
I also think a zippy secondary fabric feels rough, but it is also very effective.
People like what feels good and costs a lot.
But they are not always more effective, JMHO.