Problems I've had with phosphor bronze stings include the wearing and corrosion on the strings where they meet the pick, and the distinctly "brighter" top end of the high E and B, resulting in too high a tone relative to the thicker strings. These Tony Rice strings are consistent in sound across all strings, and have a mellowness simply not found in PB strings. The only downside to the Martin lineup is deciding which of the Retro strings to buy... that and having a pile of PB string sets that are going to go unused.