re: Ductless downdraft vent for island cooktop

It won't work like an actual ducted vent. The vent less basically uses an air filter and the recirculates the air back into the kitchen. It is up to you which option you choose and for you probably the non ducted route is best. Keep in mind more maintenance will be required, such as changing air filters (which isn't difficult). Also, it won't work as efficiently as a ducted vent, but should get the job done in a residential application.

I have only worked with commercial products mostly, but I would assume you would be fine.