Used only in "The Plan"
This FN Five-seveN (Fabrique Nationale d'Herstal 5-7) resin facsimile was made by Matsuo/Matsucorp Props. It was not used in the series proper, as these were commissioned by NBC-Universal via Propworx's principal owner in 2008. They were used exclusively as "holster stuffers" in "The Plan," were they ever used at all.
The major tell versus legitimate series variants is the extended length of the underslung "rocket launcher" on the accessory rail.