You have a point. Let me rephrase it. There are $40 quadcopters which use weak, yet easy to replace parts. More expensive parts and materials are usually easier to work with as well, so for a prototype they are well justified. But for a production model like this one, is it a product market choice to go with expensive parts, or does the cost of designing for other materials outweigh the risk of going to the customer with a more expensive product?
CDs are polycarbonate and are sold for $20 for a spindle of 100. At a pretty good profit. "Bullet proof plastic" is just marketing buzzwords.
FWIIW, polycarbonate has to be quite thick to stop a bullet and is generally used in conjunction with glass. Looking at the chart[1], it is clear it will only stop relatively lower energy handgun bullets, not high power rifle bullets. For that, it requires a glass + plastic laminate.
