340
I use only Hoppes Elite on the exterior of my 340 as recommended by a customer service person at S&W. I use BF on the barrel and cylinders and follow the directions. I'm sure some has come into contact with the DLC, and after 9 months I have noted no deleterious effect. If you have the CT grips, keep the cleaner off the lens.
I also like the Outers Tri-Care. It seems to be innocuous on barrel, cylinder and exterior.
See M&P 340 thread for more information.
How you like the M&P 340??