Me?
I kept my original M&P 340 ... which has not exhibited any problems with the lock (ILS) ... and bought one of the new ones without the lock to complement it.
While I'm still carrying & using the original one, I'll probably eventually end up using it more for "range beater" use, while I continue to try and wear it out.
I like the M&P J-frame models primarily for the XS front night sight and the U-shaped rear notch. It makes for easier and faster sight acquisition than the painted front ramps on my other handful of J's (which includes a pair of 642-1's).
I like the PVD coated stainless steel cylinder (not being particularly enamored of the titanium cylinders).
I like the stronger Scandium aluminum frame, too.
While I don't mind having the option to use Magnum loads (and I sometimes do, for quals & practice), I primarily carry some of the same assorted +P loads in my M&P's as I do my other +P-capable J's. FWIW, when I was originally testing some Magnum loads in my M&P 340, I found a couple which exhibited bullet pull in my gun, so checking each gun with each brand of carry ammunition is still a good idea, I'd think.
If I were planning to shoot a lot of Magnum loads out of a 5-shot revolver, I'd either take my SP101 DAO out of the safe or I'd pick up one of the steel J's chambered for Magnum ammunition. The Airlite's and the M&P's can be a bit rough on the shooter.
Suit yourself, though.