They are a thick, stiff, pick in a rounded-triangle shape, imitation tortoise shell, very similar to David Grisman "Dawg" picks.
The round corners don't dig in between the strings and they engage extra string area, for a full, powerful, clear tone.
This is a good pick for crosspicking guitar, in all the same ways it's a good pick for crosspicking and tremolo on a mandolin!
It has plenty of stiffness for control in down-up picking at speed.
Pick thickness, material, and shape have a tremendous effect on tone & volume.
I use these picks myself and find my sound with them to be warmer but just as loud as the Dunlop Tortex picks and Clayton Ultem picks of similar stiffness that I've used in the past.
These picks allow a strong, clear attack, but their edges slide smoothly off the strings, allowing smooth, mellow tones when you want them.