Mine came with one 12 round mag. I since have obtained two more mags for it. Not aware of any time they have been available with more than one mag, nor any 7 round mags for the M&P 22. Nor does it come with interchangeable backstraps. Although uncommon, there are a few other pistols from other manufacturers that also come with only one mag.
You will like the M&P 22 as long as you don't have unrealistic expectations. It is reasonably accurate, but it is not a match grade target pistol. They are notorious for coming from the factory full of grease so be sure to field strip and clean yours before taking it to the range to shoot it - as should be done with any new weapon. Be prepared to try several different types of ammo in it, especially for the first 200-400 rounds, to find out what cycles best (22lr semi-autos are notoriously finicky about what ammo works best, pretty much regardless of the manufacturer). Once the springs, etc. are broken in it will likely be more forgiving regarding what ammo you feed it. Be safe, and enjoy shooting!
