GI compasses are solid, a good piece of kit. However, a lot of higher end civilian compasses have a feature that I find so valuable that I haven't used a GI compass in years: a declination adjustment. In other words, I can adjust the compass to compensate for the difference between grid north (map north) and magnetic north (compass north).

I personally used to hate having to constantly add or subtract the declination amount to convert grid to magnetic and magnetic to grid. When I was a map reading instructor in the Army, one of the most common mistakes I saw was people messing up on the conversion between grid north and magnetic north and magnetic north to grid north. Having a declination adjustable compass means there is no conversion. What you see on the compass is the same as on the map. Effortless.

Also, the see-through civilian compasses can be used as a protractor as well as a compass, which is handy. I've lost a lot of military protractors in my time!

Now in defense of GI compasses, one can determine a much more precise azimuth than civilian compasses (there might be one or two exceptions, but the big brands like Brunton/Silva and Suunto are less precise in the way one conducts a sighting). Also, the GI compass has tritium (generally) in it which makes it useful even in the dark. Further, the GI compass is rock solid; a GI compass is really breakage resistant.

Personally though, the declination adjustment is so worthwhile that I've stopped using a GI compass. When I'm tired, possibly injured, and not thinking straight in a survival situation, the last thing I want to do is math. "Is this an easterly or westerly declination? OK, so it's easterly, great. Now do I add or do I subtract the declination? Oh, it depends on whether I'm going from magnetic to grid vs. grid to magnetic. Ummm..." (insert blank look of utter bewilderment here)

The KISS principle is a good one to keep in mind in a survival situation.