I used to have one (not in an RV) and I know of an RV-6 with one. What do you want to know?
 
Pete

Jon,
 
As far as I am aware it is not completely straight forward to fit an Ellison, and they can be a bit temperamental to set up, so if they run well at the top end the idle is not so good, or vice versa. When I had one I had to run with the mixture leaned off very slightly to make it run properly at full throttle. David Broom (G-RVAN) has one in his 6, and has used it for many years.  
 
Although it is more expensive I would be inclined to go with fuel injection. With better control of the fuel distribution you will probably burn up to 4 or 5 litres an hour less a carb equipped engine (I'm assuming an Ellison is similar to a carb in this regard), so the price difference and increased complexity of FI can be re-couped quite quickly.
 
Pete