When you have a variety of flat magazines the ST3 will do the job for you. Although not purely a flat magazine, the S&W Shields have a light stagger that we have fitted inside this ST3 model and that last few rounds go in a lot easier with the simple 4 step process you need for make ST3 do it's magic. Ladies especially like how it maintains a nice set of finger nails. The small shield on the lower right corner of the picture on the package lets you know you are picking the new improved ST3 for all calibers of Shields.