I have not tried PokerZebra. So why am I writing this comment?
To let you know that PokerZebra does essentially what PokerStove does. PokerStove is a free Windows application. Mac users can simply get PokerStove (for free, at pokerstove.com), and package it up as a standalone Mac app using WineBottler (http://winebottler.kronenberg.org/). It takes about five minutes.
Or, you can pay $4.99 for PokerZebra.