This is a ADCO Mag Loader/Unloader known as the Super Thumb, model STSW.
Reloading magazines takes a lot of cheer out of a day of shooting fun. With the ADCO Super Thumb Loader" you should be in good shape but you might need to bring a little extra ammo so you don't run out.
Features:
Accepts Smith & Wesson Model 41 and Walther GSP Type Magazines
Easier & Faster Reloading