First of all this is my first post and thanks for admitting me to the forum. I already own an M and P shield 1.0. and yesterday picked up my Shield Plus. I too am disappointed that magazines for the Plus are not available. My question is why 2 different size magazines are included? My 1.0 has a 7 and an 8. My Plus has a 10 and a 13. Why 2 different sizes?

Welcome to the Forum !

Two reasons for sure (I will focus on Shield Plus):
1. you have an option to carry 10 or 13 as your primary without backup
2. you carry handgun with 10 rd mag, which conceals better and have 13 rd as spare one, which conceals exactly same way as smaller one in mag pouch. No reason to have 2 x 10 rd mags.

Remember also that you can carry extra round in the chamber, so you can have 11 + 13.

For some people 2 x 13 rd might be a good option... but these are in minority, so they have to buy extra mag. And that is the reason you can buy 13rd only these days.

Magazine are available. You have to look.

Usually the smaller capacity magazine fits flush which lends itself to better concealment, and the higher capacity is extended below the frame giving some people a little more to hang on to.

I know many will carry with the flush fit and have as a reload the higher capacity mag.

Randy

Welcome. Freedom of choice.