I think, given the choice, I would much rather rely on a fully ducted chemical fume hood rather than the activated carbon filter of a ductless system. It seems that there are a lot of questions to answer about ductless systems and your operations before purchase. What is the service life of the filtration bank and how much does it cost to replace, if possible? What will the volume of work be? Given that a ductless system recirculates the air back into the room, can that pose any safety risks that can be eliminated by the installation of a ducted system? Just a few things that come to mind. I hope it helps.