I disagree with the article and think this is one of the best ways of actually understanding your product and how well it works in the real world. Don't test it like a developer. Use it like a consumer.
I think the point of the article was that that is impossible. Your real consumers have issues you yourself simply cannot have. Whenever something about the product is bugging you, you fix it. The customer is depending on you for everything.
Hell, you probably don't even have 50 employees, let alone a reason to have all 50 tax codes in your time charging system.