I have used one of these for 2 years now and have just bought another for the new baby's nursery. Personally I think they are excellent as they prevent numerous trips up and downstairs with dirty nappies to the bin. Also they are very easy to throw the dirty nappy and wipes into one handed while holding onto wriggling baby on a changing mat with the other, much better than bags in practice! I do appreciate what others say about the smell, you need to empty them every 3 days or so as although good they can't work miracles with a 4 day old pooey nappy! But then again you wouldn't consider leaving your kitchen bin without emptying it for a week and expecting no smells! Excellent and I would say fairly essential product.I have never had a problem with the cost of the cartidges especially if you buy several at a time off amazon (each cartridge lasts about a month with 1 baby).