[rented_mule]

I don't know how you'd define niche, but there are many applications where multidimensional arrays of a uniform data type are needed and data frames are not. Image processing would be a simple example where you might have 2D arrays of floating point brightness values that you want to do operations on. Medical imaging is often 3 or 4 dimensions (spatial + time). Analysis of a spatially arranged set of sensor readings over time can easily be more than that. The increase in speed of deferred evaluation is nice in applications like this, especially given that very little change is needed.

You're right that it has trade-offs, like challenges with linting. But many practitioners in these domains are experts in the area of science or engineering involved, not in software development. The ease of adapting an existing script is a big deal for many of them. Many don't even know what a linter is, and numexpr predates (by several years) the high quality linters like ruff that so many of us rely on today.