Seems like engine synchronizer gauges are going away... can anyone tell me why this is? As a boating newbie I have been told they are great, but in looking at a lot of boats, it seems like they are few and far between...

My 85 Chris Craft Stinger had one between the tachs. I don't miss that particular gauge on my Fountain. I would much rather use the room for oil temp and water pressure gauges. I can get close enough just looking at the tachs.

Listen to the motors. They will sound just like a twin engine airplane when the engines are not in sync. If you hear a waaaa-waaa-waaa-waaa sound...is it fast or slow. The slower the waaa-waaa sound is, the closer the motors are to being in sync. When the motors are in sync, they should sound like one and not two.

To the "average" twin engine boater, exact engine sync's don't really matter. Close is close enough. The guys are right they are matched by sound anyway.
You won't turn or anything wierd when 1 engine is even moderately slower or faster than the other.