The original post didn't mention anything about an EDC, but rather the were asking about bubbles and the possibility of buying a 2nd or backup compass.

I've never thought of weight as being a criteria for selecting a compass.

The primary features I look for are adjustable declination and a straight edge on at least one side.

For EDC, my preferred compass is the Suunto Gem since it has a straight edge and a rotatable bezel.