I used one with with my first and thought it was soooo fantastic, now with DD I havent used it at all and realise that it was a big waste of money.
The re fills are way too expensive and overly priced, once bubs got to 6 mths the bin did smell (when he started to eat solids).
Now I just use nappy bags i buy from coles for a few dollars (as opposed to 30 or something whatever they were I cant remember). I just put the wet nappies in the normal bin, and the soiled ones go out the door into the wheelie bin.
Biggest waste of money IMO and now my nappy bin is just collecting dust somewhere in storage under my house!!!