Hi Bob,
I guess you have pretty much covered all or most of why many of us use Wick's flags. The dual vanes make it a lot easier to read when the wind is coming from different angles, or as you say, quartering. I have always said, one of the things many shooters miss is when the flags are at odd angles with a crossing wind. The dual vaines with contrasting colors help a lot.
I'm sure there are other fine flags out there. But I have been using Wicks for years. There is a reason why many of us old timers describe the conditions as a "red condition or a white condition". Wick's flags have red and white vains. It goes to show many folks were, and are, using them.
Al