Why you need to see the media in a canister filter? It's not moving anyway
The reactor is believed to be a better, more complete way to use the filter media. In a filter bag, depending on multiple factors the bag, media will clog. Water has the property of moving through little channels through the media causing some of it to never be used as water is not moving around the media particles. A reactor ensures the media is completely exposed and the whole media quantity gets used.