I have at least two of every GT from AP-11 to AP-15. I have six AP-14's. I bought them after buying my first pair. IMO they are the best balance of noise and output of all fans. With their high static pressure they can really pull air through filters. IMO all case fans should be intake only, and all should pull their air through fans. That makes GT's the best fans to use.
To get five AP-14's for $12 each is a nice bargain.
Do put a few drops of skate bearing oil in their bearings (see my sig) to keep them running well.
BTW -- I use nothing but GT's for my 120mm case fans.