I know the Avent Express Steam Steriliser is supposed to be one of the best sterilisers out there, but I found that if I was in a rush and had forgotten to sterilise bottles and had crying baby it always took longer than the required 8 minutes, more like 15 minutes and then you couldn't man-handle the bottles straight away unless you wanted to burn your hands. I did always put the required amount of water in and even though it is not recommended put a little less water in to make it steralise quicker.
Perhaps for the organised, efficient mum this is an excellent steriliser but for the scatterbrained kind (me!) didn't find ideal and was glad to sell in car boot sale and now am expecting second any day and have purchased a steriliser more to my needs (or personality type).