I have wondered about S&W's rationale for the combinations they offer on the 340 series revolvers. If you buy the M&P 340, it comes with the XS tritium sight, and you can get it with or without the internal lock. (How many buyers would actually opt for the internal lock?) If you buy the 340PD, again, you can choose internal lock or no lock. But the sights are different, according to the S&W web site. Choose the IL, and you get a fiber optic sight. Choose no internal lock, and you get a conventional red ramp front sight.
Assuming the web site is correct, I wonder what their logic is for different sights on the 340PD depending on lock or no lock.
I've never shot a 340. My preference would be a 340PD with the XS tritium front sight, no internal lock, which is not an option. But it's entirely possible I could shoot it once with 357 and never want to shoot it again. Which is why I have just stuck with my 642 with titanium cylinder, which weighs 12 ounces even.