Iga and Koga Ryu are very well known as Ninjutsu Ryu. They used several different shuriken.
This Happo Ken is characteristic of Iga/Koga Ninja.
This Happo is thicker than the senban, and other Happo shuriken. The edges are beveled on all sides. It is also quite deceiving as it appears in the hand to be much bigger than other shuriken but its dimensions are identical to Senban and other shuriken.
According to Nawa Yumio and Tanemura shoto in their books, this shuriken is also from Togakure Ryu