Ok, guys and gals. Let's blow the foam off the beer and get really honest. First off, I'm a S&W fan and collector. I don't own a Shield, although I have a 39, a 59, and a 3913. All of these work like a marble rolling down a child's slide.
Okay... To be honest, I've never been an M&P fan, although my 1st Carry handgun was a S&W 19-3. The 'Factory Out of the Box' Shield is the only M&P I'd trust from Day 1. Mine is almost 4yrs old now. I test fired it against the XD-S and bought it before it got Hard to Find (and gained Unicorn status back in 2012).
I also have a couple of (may I say the word?) Glocks. They work and have always worked 100% for me, right out of the factory box.
My first CC pistol, after the 19-3 was a brand new Gen2 G19 in '90. Since then, I've added a G26 to the mix. They've both been flawless and would have any issues trusting a G-Word new out of box either.
I enjoy browsing on the forum, and I note a proliferation of complaints about problems with the Shield of one form or another. So I want to ask a question of you Shield owners, and I know I will get completely honest answers from you.
You've been a forum member long enough to know that complaints will proliferate, even with an exceptionally great firearm (or car, or boat, or motorcycle).
If you research the complaints and tally the unique individuals posting complaints (as opposed to REcounting all the 'Repeat Posters'), you'll see that out of the 1 Million + Shields sold, there are only a couple Dozen instances of 'Problem Shields'.
Yup... There were a couple real instances of Tolerance Stacking causing accuracy problems, 5 or 6 documented Shield40 Kabooms attributed to Ammo rather than construction and a couple dozen individual instances of RSA problems, but definitely nowhere near the problems that other manufacturers have had with newly intruduced handguns (ie: Gen4 Glock RSAs, XD-S Full-Auto recall, LC9 RSAs, etc)
The question is: Would you trust a brand-new, out-of-the-box Shield with your life?
Yup... Even if it were to have an RSA issue, it wouldn't effect its ability to go Bang every time... Even if the RSA came apart, it wouldn't "Sproing!!" until you field strip the pistol.

It would indeed fire every time (unless you hit a 'Dud' primer).