Use your unique power x times only counts the Frenzy power for Ajax. All Ajax powers are unique. This should be reworded or should count the other powers.
Bro what you are saying is true but a unique power of a hero is his/her first power that cannot changed with other spells and also can be used as invocations too.
In case of Ajax only his first Spell Frenzy can be used as a invocation by other heroes.