alt Hacker NewsI've had bad experiences with USB irons, they generally don't have stellar compatibilty with USB power banks, and when your 60W iron can only draw 20W from your 100W power bank or PSU (but sometimes it works).
They even come with these compatibility wikis of what PSU or bank to buy.
They rely on compliant power sources, so just make sure you don't use bad ones that only pretend to follow the spec.