I am sure i read somewhere that it is not as good as pplquiz, as you need to have your results mailed to you which takes a couple of days (I have never used it, and this is just from memory) PPlquiz gives you automatic feedback- questions answered correctly, pass percentage and percentage pass rate etc.
I've use Airquiz and I don't find it as useful as the Confuser. The main disadvantage is that when you get a question wrong, with a couple of exceptions, there's no explanation of the correct answer. This is find in some instances but in others you end up looking at the answer and wondering why the hell that's the correct one. It may work better for you but I prefer the Confuser with it's clear explanations of the correct answers.