I betcha in real world non-lab conditions these things can make a difference. That is what they are designed for after all. It's not the exact same thing but watch this guy demonstrate an iFi AC iPurifier in his honest-to-goodness real life system:
As fun as it is to call everything snake oil so one can feel smart and objective- the biases about audio equipment work both ways. I think arguing that the OP's thingy would only work on cheap DACs is moving the goal post. Amir-Almighty has established there is not always a strong correlation between price and design/parts quality.