Agreed, this seems silly to build your own which likely performs worse than PosgGIS and has way more bugs.

At least the article could have addressed why that would not work for their use case.

edit: also now they have to classify polygons into groups that wholly fit into some "city" polygon. That seems like it becomes a pain to maintain since you may want to expand a region in the future and it happens to go outside of your previously defined "city". Or maybe you want a region that isn't in a "city", like a "country" or "mid-atlantic" region.