It's a gimmick.
You can look at it one of two ways...
One, the flow rate is too great for the tiny low watt lamp to be effective, or, the lamp wattage is too little for the flow rate. Either way it is just not going to work on anything except maybe a free floating algae bloom (maybe). Search effective UV
flow rates for info about how much flow per watt you need for any UV
"sterilizer" to be effective.