I have the Inset a number of years now and find it very good. It is in a room that I use all the time which is great as I can use it and not switch on my gas heating. My neighbour got the hotbox at the same time as I got my gas fire and now regrets tha she didnt get the Inset as she thinks that there is more heat from the close unit. As well yu dont get the same drafts from the chimney with the Inset. I couldnt give you any idea as to running costs as I have natural gas central heating so I get the one bill.
Hope this is of some help.
Megan