These sort of devices do work. I live 200yds from our local library which has free wi-fi and am able to connect using a wi-fi dongle mounted inside a metal canister from a catering pack of beans, 4.5in dia x 7in long. I get no connection without the can. The dimensions required can be calculated from formula available on several web sites.
Amazon Fire HD 8 review: A brilliant combination of function and value – with one massive caveat