Although electric jamming devices are illegal a Faraday cage is not. "Unlike jammers, Faraday cages don’t proactively cause interference, although they do interfere with mobile reception,’ An Ofcom spokesman said.
So he's legal by UK standards and I'd have to think the US as well.
2. When Clinton was using the private email server, there was no law or policy that required her to use the government email server.
There were legal requirements. Per the National Archives and Records Administration's Code of Federal Regulations Hillary would have had to cc her official government email every time in order to maintain an official archive. Clearly she did not. This would fall under the section requiring all federal agencies to preserve records and assure the were readily available.
Mediocrity finds safety in standardization. -- Frederick Crane