I used them and loved them! So easy. I still use the prefolds, but with other covers.

They're basically just a huge rectangle of nappy you fold just 2-3 times into a smaller rectangle. Put the folded nappy into the cover (a bit like a velcro pouch) with a liner on top and bam. Very easy. Didn't leak, even baby poo stayed inside. And you can make them up beforehand, so very quick changes even in the middle of the night.