The card is anonymous, but loading it with money is not, at least not in practice - most machines I've encountered only accept Maestro/VPay (which is an improvement over PIN, as they are marginally available in other countries, but they are also tied to your identity), so you are left with the service points at major train stations at best. Exceptions were more common in the Strippenkaart era.

At least that was the situation by late 2019/early 2020, as I have not been able to travel to Randstad since then for rather obvious reasons.

Thanks for pointing this out. I didn't know about that. My experience was like that: one day I could buy transport card by cash, the other day the driver informed that I cannot but tickets by cash anymore.