Not sure what "bleed" they are referring to, but that is marketing BS. A good vinyl window, pocket insert, will do just fine in that application and should serve you well for decades to come.

Emphasis on "good".

Thank you!!!!

What bleeds/leeches/outgases from typical low budget extruded PVC windows is the plasticizers (most commonly phthalates) which are harmful and can cause PVC to become brittle.

Rather than specify more costly versions of PVC windows, I avoid the issues with fiberglass windows.