It has long been known that iron-nickel and iron-cobalt alloys form a stable tetragonal phase, the L1_0, at standard conditions, which is a hard magnetic material with a high magnetic energy product comparable to the best rare-earth magnets. In fact, L1_0 FeCo is predicted to be the best magnet of any material that has been modeled. But these phases are not stable at high temperatures, and the relaxation time to form them at normal temperatures is expected to be on the order of millions of years. L1_0 FeNi has been found in meteorites, but these are extremely rare, and the damage caused by impact limits the usefulness of the material.
In the recent work by Ivanov et al, L1_0 iron-nickel alloy was successfully prepared at macroscale by precipitation from a melt containing large proportions (on the order of 10%) of phosphorus and carbon. This is the first time that bulk L1_0 FeNi has been produced on Earth's surface. This potentially opens the door to producing strong magnets from just iron and nickel.
For a sense of scale, annual nickel production is about two million tonnes per year, while neodymium production is less than ten thousand tonnes per year, with neodymium representing a fraction of that. The material availability for producing strong magnets therefore jumps by more than an order of magnitude.
IIRC, Polymagnets give unique field patterns but do not replicate the overall field strength of neodymium magnets.
A much better alternative is someone like Niron Magnetics, who build nitrogen-doped iron magnets that demonstrate field strengths that are (roughly) equivalent to rare-earths:
https://www.polymagnet.com/