The problem you are going to have is anyone who believes this could function as advertised is not going to understand/ believe the basic physics principles behind why it will not work.
For a start, lets be absolutely clear this is 100% a scam. This device is clearly some old USB thumb drive or adaptor of some kind, I tried to use google lens to identify the PCB image from the silk screen "AB5-18" but didn't get any exact matches.
On the one side of the PCBA it looks like whatever IC/ electronics was originally fitted has been removed (probably so it doesn’t draw current). All thats left is a few resistors, MLCC's and an SMD (D1 identifier), you could plug this into a USB charger and see if the LED (D1) comes on just for giggles, it wont do any harm, its only very low voltage. On the other side its very difficult to identify what that is, but if as suspected its got no electrical connection its doing nothing, its not attenuating EMF around the home that is for sure. It does appear to have a label or tape over it, if you remove that it may well show you identifiers or markings you can google, odds on its an eMMC IC.
The only way to reduce the magnitude of electro-magnetic waves is to either cancel them with an identical signal 180° phase shifted or block them ie have a faraday cage or some RF absorbing material between you and the source. Clearly, if it uses no power it can't be doing the first (although there are many other reasons why this "device" couldn't do that too) and its definitely not magically putting a physical cage around the house.
@RobSm88
Have you tried getting a signal analyser app (net analyser is one) for your phone which gives you a dB level for the cellular and wifi signals your phone sees ? this would be a very simple demonstration to your mother that these signal levels do not change when the device is plugged in or not or even in the room etc.
If it helps, I have 25 years experience in the Satellite Communications industry making high frequency radio transceivers (and have a BSc in Physics) I'm probably qualified to comment (or am I part of the cover up !!!!!
) .