In addition to being cheaper, tint would be more effective, more stylish, less effort, less risk of breaking something, less impairing of your rear view while driving, no risk of rattles, and of course cover your side windows in addition to your rear. Use F1 Pinnacle Ceramic 35% -- looks stylish yet subtle rather than going over the top on blackout, and ceramic doesn't impede electronic signals for Comfort Access, remote, etc.
'16 Cayman GT4 (delivery pics
Gone but not forgotten:
'11.75 M3 E92 Le Mans | Black Nov w/ Alum | 6MT (owned 5/2011 - 11/2015)