What's cursed about this? <i>Operational</i> amplifiers were specifically designed to perform mathematical operations. If anything all the other uses today are the cursed ones (especially as comparators).
The post says "Unfortunately, in introductory texts, their operation is often explained in confusing ways." and this is 100% true. I remember being baffled by them in high school (when I was taking an online college-level EE course). The blog is a remarkably good explanation.
I was wondering about this as well. Now I would like about the performance of that multiplier and what kind of multiplication to expect from it (4-quadrant?), but the summing, subtraction and integrator circuits are bog-standard and the first present in most analog signal mixing.