A differnet point of view.
The SD trigger is usable in stock form, and people who come from a revolver background find it just fine.
People from a 1911 background, or who just like to modify their guns, are often very vocal proponents of the apex kit.
As someone who instructs beginners, I encourage people to learn to shoot the stock gun, expecially proper grip and trigger control. Then wait until you are a seasoned shooter with experience and opinions of your own and decide whether to buy an M&P Pro or modify the SD or whatever.

Especially if money is tight.

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Science plus Art