Polars is a dataframe library. Yes, it features vectorized operations, but it is focused on columnar data manipulation, not numerical algorithm development. I might say that this is narrow framing, people are looking at Julia through the lens of a data scientist and not of an engineer or computational scientist.
Most "data scientist" code is exploratory (it's a prototype or a script for an one-off exploration) in nature. And my main gripe is that making that code production ready and maintainable over a long period of time is so difficult that I would switch to Rust instead. If I were going to switch to Rust, I might as well start with Python.
afaict, for that project they never went through PCI compliance. See original thread for more information: https://news.ycombinator.com/item?id=40228751
They seem to not have a lot of real world experience and/or throw caution to the wind and YOLO through security practices. I'd be weary using any of their products.