They're brand names....
Perspex is less well known...but mostly used in signage...
Perspex I'm fairly certain is acrylic but not all acrylics are equal
It has good optical qualities...I heard about it from mazda using it for the dash panel of one of their cars....it looked black when the car was off but the lights were hidden behind it...It's more expensive than plexiglass on average...
for templates you could probably live with cheap leftovers from a sign shop