This is fantastic! We're building a walk-in-closet-sized Faraday cage at i3Detroit, though of course we're in the US so we won't need it for this specific hack, there's a zillion reasons it's fun to have one!

Off the top of my head:

The biggie is that we're right down the street from WOMC's transmitter, which is 135,000 watts EIRP. It gets into EVERYTHING and makes other RF measurements more difficult, so if you're trying to align an amplifier or something, it's nice to start from a quiet place and get the basics solid, and only THEN add sources of potential intermod and stuff.

Debugging wifi, bluetooth, and other wireless stuff without a zillion other nodes in view. Yes you can filter the output of a sniffer, but it's more fun to filter the input. ;)

Lighting up a 1G or 2G cellular network without worrying about spectrum licensing.

Practicing offensive wifi techniques or other stuff that might interfere with the hackerspace's existing network.

Playing with GPS spoofers in an FCC-free zone. Or anything else you might find amusing but want to do responsibly.

Locking an iPhone in there to see if it reboots itself... (rofl)