Acrylic is prone to fracture if not cut properly and in high vibration machine guard applications it's not well suited.
In our product, what helps is that the acrylic is thicker (a quarter of an inch) and then laser cut (whereas machine cutting introduces micro fractures throughout the cut). Another thing that we noticed is the way the fastener points are cut out, designing in broader fillets instead of sharp edges helps tremendously. Finally using plastic nuts instead of metal helps with accidental over tightening and putting warnings in the instruction manual helps too.
Why not Lexan instead of acrylic? The driver is cost. When we did the market studies the BuzzBox suddenly become out of the reach of most maker budgets.
We built a prototype earlier this year that is still in use today, hundreds of prints with an Afinia H479, with no fractures to report!