Marco Leon wrote:
A pilot friend insists that there is a fundamental difference in the
way these two systems operate. I am thinking about installing an
autpoilot and since I have the extra panel space, I would like to get
the System 40 or 50 for (what looks like) a more user-friendly
interface. However, he claims that the newer System 20/30 is better
at handling its duties in a number of different aspects.

Can anyone point me to an article or maybe share their experiences?
Google turns up nothing.
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I don't know, Google worked pretty well for me:
http://www.s-tec.com/prodbrochures.html The differences should be pretty
clear after perusing their product brochures.