I have used them on occasion. They're good for when:

DS needs nappy rash cream
DS is at nursery - they can just flush the liners and I don't get old poo to deal with
I can't be bothered cleaning a nappy (ie I'm ill - DS doesn't get on with disposables so flushable liners are the way to go)

They are about 30p a sheet so not inexpensive but it's fantastic when he poos and I don't have to clean it off! Also cuts down on the washing a bit.

I use re-usable fleece liners about 95% of the time, but sometimes a paper one is what I need. I get mine from the local pharmacy.