In my 100% totally personal opinion the Ghuizhen tech from Kechibi Code is broken drek and should be ignored. YMMV.
But RAW, there is no "to hit" roll. Target(s) roll Body plus Will to resist the effect. The effect is determined by the weapon used, and the setting or how many charges are spent. The sidebars on p. 86 and 87 spell it out.
So a Flash Scope will do 10s to a Target, the Target rolls Body plus Will to reduce, and Blinded and Dazed statuses are applied depending on the details.