So here is mine on the left with the one that you are looking at in the middle and on the right is a typical sized puka shell necklace.
Here are a few close ups of the shells. The huge one has much rougher shells, some are not sun bleached and still rather rough. The one that you are considering has very smooth shells that are very white. All of this from being tumbled in the ocean and sand and bleached by the sun. As you can see the size of the actual shells is very close, it's just that my rustic one is twice the length.
Here is a close-up with the typical puka shell necklace. See how fine the one in the middle is?
So mine is long and huge, but low grade. The one on my website is much higher grade shells and similar in size regarding diameter of the shells.