I wouldn't call ASML's products complimentary. They are the only machines capable of EUV lithography. Without EUV, nodes smaller than 7nm wouldn't be possible. But even before EUV they were the leading manufacturer of lithography machines. They deliver to all the big players like TSMC, Samsung and Intel.
They are so important/valuable that the US government is negotiating with the Dutch government to ban ASML from selling EUV machines to China.
I remember bridgewater shorted ASML for big positions for no reason and then the news broke out that US government banned ASML from selling some stuff to China.
ASML has a monopoly on Extreme UV lithography machines which are needed for top end chips. So it's a pretty good picture of where investment in chip fabrication is heading.
They and TSMC are one of the hottest companies that additionally do hard engineering instead of social medias or ads