OK I will try to answer your question but this will merely be an opinion. I own the 40 fullsize as well as the 40 compact that I carry daily! I also own three 9mm's two full size and one a subcompact!

The recoil of any 9 mm to me is kinda like a air bb gun which is not really much but the 40 is snappy regardless of its size. A 40 caliber handgun will recoil upwards where a 45 will push back this make getting your sights back on target more difficult with a 40 caliber gun.

I once owned a 9mm KelTec PF9 which I traded for a full sized 45 M&P mostly because I just did not like the little gun and its grip in my hand, so I guess a Shield 9 should not be that difficult to control.

I look at a 9mm like a good gun for getting used to the recoil of any weapon, but I have been shooting pistols since 1974!

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59,M&P9,40,40C,357,(2)45,G26