I'm an EE, and also a very cheap sort of guy. So, the combo led me to investigate the BSFC of the various mixtures I was running. The EGT kit allows me to see basically the same as a O2 sensor on a car. In fact, since I have a 6 probe EGT, it could be said that I have an even greater advantage since I can see the products of combustion efficiency on each cylinder.
Now, I'm prolly one of those guys that thinks he can do better than the computer when it comes to mixture control. I have the BSFC curves for my engine, and found where the factory(back in the 40s) set their data points, and where the best efficiency is found.
Now, based on three flights where I very carefully calculated the fuel consumed by replacement, and the engine run times, and the RPM, and MP for this engine, I actually worked at a lower BSFC by controlling the mixture than the factory numbers indicate. Of course, the engine was running lean of peak, and that I had the plane barely running smooth but yes I think I beat the system.
Now we have nothing to measure against because I don't know of anyone who has a FADEC system working on my engine. Could they do better? Well, what is 'better'? When I need full rich for take off, I select full rich. When I start into cruise, I lean carefully to maximize efficiency. When I'm in cruise, I run lean of peak.
The only thing I'm missing is a detonation gauge. But then again, a single detonation event can be pretty bad on a plane engine, so I don't want to operate that close to the detonation margin. I would think, but don't know that any kind of computer driven aviation mixture would take into account to avoid detonation margin by a significant amount. If that's the case, I can see where I could do as well, or better than an automated system.