I was thinking about this and the Air France A330 that crashed in the South Atlantic tragic loss of control due to instrumentation issues, while I was reading an article in Defense News about the F18 crew who recovered their plane after suffering from a major A/C problem that caused their cockpit & instruments to ice over. It is reported that they were able to recover the plane because they had a Garmin watch which provided basic speed and altitude information.
As a card carrying member of the SLF there does appear to be some logic to having a completely separate system available when all else fails.