I guess the short and skinny on what ProMod does is allow more variation and skill into saber vs. saber combat through the Combat Strength Crosshair and the bonus meter systems. The old system's blocking and saber hit-detection systems were so laughably broken that I felt compelled to fix them. I won't go into the specifics. I've detailed all the flaws of the official versions in many other threads, and in my old strategy guides (www.oculis.org/asc
The best advice I can offer you for learning what ProMod does is to drop by my official server or the Praxeum Knights server while some of the regulars are in there at night. They've got a deep understanding of how the game works, and are generally ok with explaining the mod to new players. I may be in there myself from time to time.