It works. You'll need to train in defense and reflection. Defense will have your colonist dodge more. while reflection will have a chance to make projectiles (minus explosive rounds) fly back to pirates and tribals.

According to stats, one of my colonists has ~180% deflect chance. I'll keep tinkering, perhaps mods with weapons act differently

If I recall correctly, the deflect chance only applies to a successful block. So if the colonist fails to block the attack, then they don't roll for the deflection.