I am also an engineer by trade (now on the dark side - project management).

Pro for metric: simpler maths (no fractions!), easier setup, and most plywood is 18 or 19 mm.

Pro for inch: scale of inch is easier to us for large projects like house just due to inch is such larger size than a mm.

In the end, woodworking is fitting and templating and the scale does not matter a whole lot unless you are setting datos or fitting slot widths. Most of the time i am cutting up on a line and smoothing it out with finer tools such as a hand plane or sander. After it is is more the resolution of the tool's settings.

just my 2cents.

I live in the US and as an engineer, I design things at my job in both metric and imperial units.

What are the pros and cons of going metric while woodworking as a hobbyist in the US ? I am asking primarily because I am ordering a Hammer A3-41 jointer-planer and need to choose the dial indicator.

Most engineers I know seem pretty sharp, and can work in either SI or imperial.

Can one order the other the imperial dial indicator and fit it after the fact if they do not care for the origional SI dial indicator?

I had an A3-31 when I first got interested in Felder J/P's in 2008. I would suggest you might look at a Wixey remote digital readout and have the best of both worlds. If you want a more robust unit than the Wixey you could also look at Proscale. I now have a Felder AD951 that has factory digital readout and the ability to switch back and forth is a nice option even though rarely used.

John

I fitted a Jet JJP12 combo machine with an iGauging DRO.  I could work in either metric or imperial, however I found that Liked decimal inches for planing wood.  I use metric and decimal inches interchangeably but still don't do fractions 

For me decimal inches is the best option, easier math and can still communicate dimensions in a terminology common in my culture.