If you're located in MA you'll want to be careful about buying a "new" kit that includes all or most of the magazine components. This has been an issue in California recently.
There are many generations of Glock magazine which will all work in any pistol - an old U-notch style will work in your Gen4 pistol. If you have a new Gen4 15rd magazine in MA good luck to you I guess, I wouldn't hang on to it unless you're an LEO. The NES community at large tends to frown on violations of the actual MGLs (ie not Mad Mauras unilateral decrees and judicial fiat) and the magazine capacity ban is actual law.