ALL
britax seats have the 1 click mechanism. Or they did until they redesigned the buckle to fit what every one else was doing. It never bothered me...I just knew that's the way their seats worked...it's even in their manuals.
When you hear the click, you know that both tongues are secure. It was just their way---they've led the market in other areas---such as higher weight harness and now the other companies are following suite.
Susan