Among others I've been looking at this brand for wick style indoor petroleum lamps. Ive looked primarily at DHR (Den Haan Rotterdam), E.S.Sørensen and Delite. From what I can tell the biggest difference compared to cheaper lamps is that these will use round wick Kosmos style burners or double wick Duplex burners. This will obviously provide better and brighter light. These more expensive lamps will also use proper high temperature resistant glass, which cheap no-name lamps might not always do.
I will definitely get one or two of these lamps in the near future and when I do I can report back if you like. Although I will likely be getting table-style lamps for indoors and not outdoor lanterns, but they might still be indicative of the brands overall quality. Frankly I'm not sure how useful my insights could be since I would have no point of comparison to cheaper alternatives.
The majority of the high price tag will come from the fact that most of these lamps are manufactured in the EU, and that these professional style petroleum lamps are likely a small niche market with low margins and turnover.