Are longboards from Walmart worth buying?
Sure. They are all fiberglas over the same closed cell polyurethane core (used to be Clark Foam, but now closed.) Or, go on Craig's List and get a better , used one for same $. A few dings machts nichts. You Will ding your board, anyway.
Some retailers such as ALDI and LIDL have a reputation for great quality at low prices. Others, such as Walmart/ASDA have a reputation for low-priced crap. Not saying what you’ve seen is poor value even at a low price, but their track record suggests not. A deck which snaps or trucks which break can cause severe injuries or even worse. If you buy then don’t push the gear to any extremes and make sure to wear full safety gear.
It's Walmart, you'll get what you pay for and sometimes you'll get less than what you pay for.
you get what you pay for
It is a crap shoot. Go ahead and try one.
A used proven board is better than a cheap useless one.