Tried to use this attachment once but with a hoover connected it makes the whole multi-tool cumbersome and unwieldy. I used it with the sanding attachment and still managed to get mouthfuls of dust.
Not convinced this is a 'must have' piece of kit.
If you already have a DeWelt oscillator multi tool, this dust extraction is useful when you sand the wood. But a dedicate sanding pad adapter, holed sanding papers, an 1 1/4 inch hose and a vacuum cleaner are needed, costing to get a fully equipped system.
Most of the reviews I read were not very encouraging but it’s Dewalt so I ordered one and as long as you use the sanding pads with the holes in them it is not too bad