I have an EDM 760 in my twin, and it has been very useful. First, it
immediately can identify a fouled plug, or plugged injector. This saves a
lot of time searching for and cleaning plugs when the engine runs rough on
one mag at runup.

It also helps in mixture management when leaning, and helps to protect the
engine regarding the CHT's.

Fuel flow is also a bonus, particularly in combination with a GPS that will
calculate range, endurance, etc.

Overall, they add a lot of efficiency and safety.