and with some airlines introducing wi-fi onboard I'm wondering to what extent - if any - safety is compromised through their use.
Standard tests are carried out to try to ensure that they don't affect aircraft systems, but like any electronic devices, they can develop faults which are unexpected. Even thoroughly tested Inflight Entertainment Systems (on and off-wing) have interfered with airplane systems. Even though, in many cases, the system problems are only minor, they may cause distractions at critical times.