The main difference in how the two work:
Germ Guardian: dry heat
Avent IQ (and the new Nuk sterilizer): steam
Germ Guardian does not reach a high enough temperature to sterilize, esp. to kill germs on surfaces that have gone in wet (which is not it's intended use.) Steam (these sterilizers reach 212*) is a proven method of sterilization.
Mom2Lillian posted a link from the CFF on this thread in adults: <a target=_blank class=ftalternatingbarlinklarge href="http://www.youtube.com/watch?v=R0Drtlo7XFA">CFF recommendations re. steam sterilizers </a> This is specifically in reference to cleaning the Altera but steam sterilizers get the OK from the CFF here. <img src="i/expressions/face-icon-small-smile.gif" border="0"> I was so happy to see they finally officially have something to say about this! The NUK is featured but is not stated to be the only approved choice.