My yellow potato onions have been ping pong ball sized at the largest.
Andy’s green multiplier has a much thicker stem so I’m guessing bigger bulbs.
Bought assorted seed on Etsy “ Potato Onion seeds ~ Open Pollinated Heirloom Multiplier Onions” fromfullskyfarm
They are thickening up way more than my standard “yellow”. Mainly germinated yellow/brown with a few white, and a couple red potato onions out of 100 seeds