Things I liked:This mag works flawlessly and it should since it's part of the great Maruzen Walther P99 Fixed Slide system. This additional mag allows the mag to warm after adding gas while alternating use with another mag. Things I would have changed:Nothing. A little expensive but quality usually is. What others should know:This magazine is only for the Walther P99 FS Green Gas pistol and not other P99 models.