The Okna price is VERY low. Who is the install company? $369 per window completely wrapped and out the door (if I'm reading that correctly) is insanely low for one of the top window choices available. I would be sure to ask details about the installation and thoroughly investigate the dealer.
Is it possible the installer is cutting corners on the install? Are there ways to do a substandard install and not incur the typical costs that a quality install would?