Spinel is a transparent ceramic material.
Spinel transparent armor is 50-60% lighter and thinner than traditional ballistic glass.
Spinel is also extremely abrasion resistant and has excellent optical properties.

I would like to see how well it stacks up against the AP, API, or Raufus rounds.
I'm guessing it doesn't, that's why they were using standard FMJ ball ammo.
But to Spinel's credit, I doubt the thicker Bullet Proof glass would fare any better against such rounds.