I have one on my 220g. At the moment I have it hanging on the side of the tank running off a sumbersible pump inside the tank but I have just finished setting up my new sump and will be setting the FBF up to run off the sump return and then recirculate back into the sump.
What I heard about them is that they are very efficient biological filtration for the size and flow rate. They recover better and more quickly than a wet/dry after a power outage situation, and they handle sudden increases in bio load better than most other systems. The last 2 points I read are a result of the type of bacteria which colonises the FBF. Due to the constant movement of the sand grains(bumping into each other) the older and dead bacteria is removed from the media and replaced with the newer younger bacteria. This means there is always a large population of younger bacteria which are able to multiply more quickly than the older bacteria?
Again this is just what I have read so I dont know how much of it is theory or how much is proven fact?
I have pic but its very crappy, will get a better pic soon.