Why is the Integral Lighting IL600 a half round shape?

Integral Lighting designed this hardscape light to simplify installation. The half round design of the insert is to make it as easy as possible for you to insert after expanding the joint of two hardscape layers by plunging a standard 7″ masonry blade into the joint.

What material is the IL600 Series constructed of?
Does the IL600 Series require drilling for installation?