I can't compare Cow Horn to Tortoise as I have never even seen a tortoise shell pick. I've always used plastic. My friends live in Montana, just moved there from here, but drive truck up there most of the year. As soon as they get relocated I'll ask them where it came from for sure. After I got it I got to thinking that every time the horse shoer comes he leaves a bunch of potential picks laying out by the barn.
Since I just got it I'll be curious to see how it lasts. I do like the sound. Although I am experiencing a delay in that after I play it for a bit it starts sounding better. Kind of limp or dull at first - but after a song or two - very nice.