So a quick search online shows that two-blade or four-blade fans are most common. I ordered a four-blade Voda stove fan which I found on eBay here. It arrived quickly and I was pleased to see that all the packaging is recyclable. A card outer box with corrugated card insert that safely held the fan in place, no unnecessary plastic bag or moulded plastic holder.
It was quite warm in our house last night, so we didn't really need a fire, but too impatient to wait for a cold morning or evening, I placed the fan on the back of the stove as per the instructions and waited.
Mr J and I sat and watched the fan waiting for it to do something as the stove warmed up, a slight touch by Mr J started the blades moving and it merrily spun away until the fire died down and the heat given off by the stove lessened. It was very quiet, I didn't notice a whirring sound (which had been a slight reservation of mine) or a tinkling noise at all. The idea behind the stove fan is that it whooshes the hot air away from the stove further into the room and distributes the heat more evenly, so you don't get that 'burning front, freezing back' issue.
Did it work? Yes, it seemed to move the heat around the room very well and we could feel that the warmth was being pushed further away from the stove. Job done! I will be ordering another stove fan to use on the wood burner that heats the kitchen and snug (one of those stoves with doors on both sides) as the kitchen doesn't have an alternative source of heating.