Correct; I would not fly with just one electronic device holding the approach plates etc.
There are certified EFB products but
AFAIK all are dual so if one packs up the other pilot has a working one.
Personally, I print off plates for dep dest and alt, and enroute chart sections. This is not a big deal; one prints them off 2-up double sided i.e. 4 pages per A4 sheet of paper.
The unavoidable situation is if you have to do an airborne diversion to somewhere unplanned, and then you have just the the
electronic representation of the approach plate. If that failed, your only option would be a radar letdown to a VFR landing (an SRA, in effect) or an ILS. For a radar vectored ILS you just need the runway heading and the ILS frequency. How likely is this? Not that likely. But IMHO if you always flew with everything hanging on a single electronic device you will sooner or later get caught.
One cannot backup everything but one can guard against failures of two independent systems.
The thing which an electronic product like Jeppview does for you is that you don't have to print off plates for everything imaginable.