From publisher blurb:
Has spellcasting grown stale in your game? Aching for the cool effects and team dynamic casters could bring to the table in older games? Do you wish mage-on-mage fights could have a sense of dynamism and scale fundamentally missing from the game?
We've got you covered. Enter a dueling system for 5e! This easy-to-resolve mage dueling system allows your spellcasters to layer additional effects on to their spells at the cost of limiting who it is they target (namely, the other person in the duel). This tradeoff makes for interesting scenarios in which your players can participate and impact the outcome of the duel.
Because certain effects can change the battlefield depending on who's caught in them, this gives the other party members an opportunity to participate in the duel the way they couldn't with typical spellcasting. They know who must be targeted by the spells cast by the mage, and can move around and manipulate events so as to maximize the impact of said spells.
Though additional rolls are still being made, the teamwork element allows the party to become invested in each resolution, and provides another mechanical incentive to pay attention.