I know I quote this ad nauseam but ever since I bought one each of brand new Uni and Twin Air filters in order to compare them, and found that on holding up to the room light I could see hundreds of pinpricks of raw light right through the flimsy foam of the Twin Air, I lost all confidence in Twin Air 'filters'. I'll throw it away before ever selling it to anyone, but I want to keep it as an example.
ps. the Uni, held to the light and eye right against the hole, was black as a tomb.