I used them for 6 months but haven't replaced them. I was very impressed at first and saved a fortune on washing powder.
If you're just 'refreshing' clothes rather than cleaning to get out food & stains then they're great.
I have found though if you don't get the clothes dried very quickly after they've been wash they smell quickly. So its been a bit rubbish with a wet summer, not able to line dry and not having heating on to dry quickly on the radiators.