Got a no lock 640-1, & a no lock M&P340 (bought new 3-4 years back) myself. Both loaded w/ 135 Gold Dot +P / SB.
The 340 gets WAY more street time (EDC), & the 640 is my bump in the night piece. Both are excellent weapons (zero buyer's remorse), & I'd REALLY hate to do with out either.
I considered the 442, before purchasing the 340. The 442 is I'm sure, a good gun for the money, but price differential aside, I believe the 340 to be a much better built firearm.
I view it as seriously overbuilt for it's intended purpose. And overbuilt IMHO, is worth paying extra for.
Had I been seriously strapped for cash, & in need of a pocket pistol, I'd have bought the 442 -, hoping for the best. I'm far from affluent, but although admittedly a bit on the pricey side, the few extra bucks for the 340 just didn't seem like that big of a deal - for a weapon that was to be my first line of defense 90% of the time. Of course, that's just me.
Greenback dollars come & go like the wind, but top quality defensive firearms seem to stick around...