One difference was the Alcoa alloy used. The 6006 Master frame was a fair bit softer than the 7005 alloy used in the Pro. The rounder cross-section of the Master and Standard and Edge kept them flexier compared to the angular design of the Pro and later Vector. The Standard alloy was soft in play, but somewhat brittle, easy to break. We saw a few broken in the neck area 'back then'.
Most(if not all) Standards were pre-strung...blue spiral nylon. Really a decent stick compared to some of the metal offerings of the mid-late '70s. One of the top men's doubles players in South Carolina used the Standard in high school and kept using it into his twenties.
I recall a SMU for Herman's World of Sport that used a different color throat insert and grommet strip, also...pretty sure it was a Master in disguise.