I'd never heard of a recirculating downdraft but if it does exist you'd be getting the worst of both possible worlds. Are you not allowed to vent outside or is your current design not amenable to it. I'd look at redoing the design if possible. An overhead recirculating vent would be somewhat better but in an island setting I almost wouldn't bother.

Berbel extractor hood has the best recirculating technology but currently only available in Germany and UK.
In conventional hoods grease is absorbed in filters. Grease particles clog the pores of the filter, and hood performance is reduced in increasing proportions.
With the berbel principle grease is accelerated out of the air by centrifugal force, and is effectively separated at two points.
The interior of the fan box remains virtually free of grease particles. There are no consequential costs, no unpleasant odors, no vermin, and there is no fire hazard.
With berbel the unit can be cleaned with just one wipe, as easy as cleaning a Ceran hob.
The stainless steel tray is made of the highest quality stainless steel and thus is dishwasher safe.

http://www.berbel.de/int/index.php?id=300351

http://www.berbel.de/int/index.php?id=10