I just went thru some wiring on an installation of a Garmin 250XL
electronics device. Somewhere in there is a comm, nav, display, data entry
device and I think there is a roll of toilet paper in there somewhere. If
this thing can do all that the manuals say, you better not try it in
turbulence and instruments. I had trouble finding the switchology to just
do comm. The helicopter panel where this is mounted would require the
passenger, and a knowledgeable one, with the directions in one hand to bend
over and read the display and operate the controls.
As a retired electronics engineer, I am aware of the penalties for having
one box do everything. Yep you said it: Single point of failure. That and
the instructions and switches become hard to use in a bouncing aircraft. If
a device does everything, the chances are that with compromises needed to do
everything, it doesn't do any one thing really well. This particular Garmin
does not lend itself well to a small helicopter environment where there is
rarely more than one hand for a short period of time available to play with
mode switches. Far too much data displayed simultaneously that requires
reading not just scanning.