Main purpose is to save space around printers. Don't forget to plug filament buffer between holder and MMU2/MMU3. 

Main spool holder segment fit mk3s build space and it takes aprox 0,5kg from filament. Parts are mounted with standard M3 screws.

Easily expandable with more segments. When printed from PLA it's recomended to fix it on wall otherwise weight of spools slowly deform base (seen on photo with spatula bellow base part to avoid tilt to front) .