Not picking on your M&P as I like it, but a couple things pop out at me.
The fit of the side plate and the kind of rough appearance of the cylinder makes me believe the gun has been refinished.
I can't quite tell, but the trigger and hammer appear to have the same finish as the rest of the gun when they should be case hardened.
The bottom side plate screw has a flat head when it should be rounded. If you remove the grips, maybe the proper screw is there and you can swap the two out.
This is a "transition" model that were still using the long action hammer which would be soon be replaced by the short action "speed hammer".
Many shooters prefer the long action.

If everything I wrote is true, the gun is not a "collector piece" but if it functions reliably I think it would be a way cool carry piece.

Hope this helps.

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Cheers!