What is a connecting mullion?

This is the connection between multi-panel casement windows. Conventional windows are connected side by side because they are manufactured separately (i.e. a conventional double casement is actually 2 windows connected together). You've probably noticed how thick the the connection is between multi-panel casement vinyl windows, 7"- 8" on average. Magic Window is different, our multi-panel windows are actually manufactured as one using our patented Common Mullion system. This results in a much thinner connecting mullion of 4", what would you rather look through?