RE: Elec. Advance versus Mech advance
A magneto is an self powered electronic system.
What every body is calling an Electronic Ignition (EI) is a battery powered ignition system.
The magneto has fixed timing, the timing BTDC does not change with RPM. There are EI's that also have fixed timing.
For best performance the engine needs variable timing. less advance at lower rpm and maximum advance at full throttle. The maximum advance needed for max hp varies from engine to engine.
An engine does not care how the variable timing happens only about the amount. At idle and full throttle the mech adjustable timing and the automatic timing will be the same.
In the mid range they are a little different, not better or worse just different. Which one is for you depends on what plane your flying and how you are flying it.
90% of the fliers can't tell them apart.