"The characters within both subfamilies, Sans & Mono, maintain the exact same width across all font styles, independently of the values set on the Weight, Casual, Slant, and Italic axes. You can therefore use Recursive to create animated font transitions without breaking the layout of UI elements like menus and buttons."

This is a useful feature - is it common in other fonts?

I certainly have run into problems in HTML with bold text causing button widths to change.