Tempered Helm should give +3 to strength, +5 to DR and inflict -5 to Deflection per kill for 20 sec. However, when Zahua kills somebody, helm gives absolutely nothing. There is no message in combat log that Zahua affected by helm, and might and DR do not change on character sheet. And for some reason these bonuses are always suppressed.
Here's autosave in 6-th level of Endless Path. Just let Zahua kill the skeleton fighter.