D'Addario have great things to say about these strings. Their language is a little sensationalist for our tastes so we will paraphrase.
The high-carbon steel core means:
Less likely to break;
Louder mid-range (even before plugging in);
Better tuning stability.
Here at Foulds, three out of four staff members have converted to D'Addario NYXL and refuse to use anything else.