Well, from my limited experience, Plexiglas is clear like glass. So is that Lexicon stuff. This material I'm talking about has a very slight texture to it. You can see thru it fine but you can defiantly tell it's not your normal clear plexi.
Also, countersinking screws holes or routing edges of plexi is tuff to do without melting or cracking. Which leads me to wonder what that stuff was...