I have been using Martin's new MSP+ (coated clones) for about three weeks (note the "long-lasting" remarks below)

Here is Martin's marketing hype, my opinion follows. . .

"Our new Martin SP+ Extended Life Strings are specially coated offering a clear, rich, and long-lasting sound as well as numerous benefits, including protection from moisture, salts, perspiration and other contaminants. In addition, the new SP+ coating helps insulate the wrap wire to prevent corrosion between the core and the wrap wires. Martin uses computerized equipment in a climate controlled environment to verify the high tensile strength of all incoming wire prior to manufacture, The brass wrap is then carefully spun onto the core wire for the four wound strings of each set. SP+ strings use the same special brass plated core wire that is incorporated in the innovative SP string, but the brass wrap on the four wound strings is specially coated. Finally, the surface of the string feels smoother and faster for the player. SP+ strings are available in either 80/20 Bronze or 92/8 Phosphor Bronze in either light or medium gauges."

I liked Elixirs alot on cheaper guitars I owned, but for some reason, they sounded awful on my martin, so I was interested in these (SP's don't sound any better than several other brands, have a very short life and transmit "skin squeak" more than they should, says me).

My opinion, for what it's worth; SP+'s offered not one iota of improvement over SP's except they last a bit longer.

Bob P