How would this work for the ninja? would round per level abilities be active for four extra rounds?
I thought on this too and i think it would work like for a monk, only with CHA instead of WIS of course. Else like similar items for fighters and the like, you dont get new abilites, but the ones you have get stronger. So four more rounds, yes, and of course two points +DC and ki pool. Why not?
You can convert ki mat the same way, just exchange WIS with CHA.