Here's my take on what I've read here. I don't own a welder of any brand at this time.
My understanding from working with an international boiler manufacturer back in the '70s is that UL and CSA are agencies that give a yay or nay on approving certain electrical items and other items but do not endorse or recommend one item over another. Their mission is to make sure that the item or number of items in a component PASS an inspection for the item/component to be used for a particular purpose with a specified AC, DC, plug or similar. This is a serious business, and non-compliance, or lack of a UL label can stop a product from coming to market. It seems to me that if, for an example, the wiring for a particular welder, dryer, or other 240V appliance is ambiguous as to what plug should be used, AND the same appliance has NOT PASSED the UL lab tests, AND/OR the approval process has denied an approval because of concerns for safety or other factors within their jurisdictional scope, a bogus, fraudulent labeling of the product must be resolved, and consumers who bought the product in good faith must be made whole by the product manufacturer, especially if somewhere in the manufacturer's scope of responsibility they were aware or made aware of the issues.
The difficulty comes in enforcing the manufacturer to take responsibility, especially in today's cut costs to the bone mentality, and often deny, deny, deny, until they are forcibly held accountable.
For example, in the news currently: GM ignition switches. How long? Who knew? When did they know?
Is a %age of original product cost a fair deal to the consumer who is out a welder? Want more? DEAL DIRECT with the company and get what you can, or sign onto a class action if one ever arises. Otherwise it's like spitting into the wind.
The UL label does NOT mean you can't get shocked, or die, or anything other than a standard set of tests have been passed and the product is approved to be sold and used for it's intended purpose.