HumX works well for what it does. It breaks ground loops. Yet, it still acts as a safety device to open the circuit if to high a voltage is present on the ground. I use 2 with my Audion Black Shadow 845 amps that have internal ground issues that populate into ground loops when tied to the whole system.
Cant say anything about the Ifi. It appears a filter like any other Shunyata, Isotek, AudioQuest. The Ifi data is saying passive filtration starts working at 1M hertz. This is not true. I know Torus transformers start working well at 50K herts. Very similar the the IFI. And a Torus is a dead stop to DC. But, the Ifi is only $109 and I have heard other plug in devices that do work. So I would assume the Ifi is getting rid of some amount of noise