Also, you can try out the service without paying for it by just visiting the site and seeing what it says about certain stories you know about. So I'd suggest just doing that. You might not get all the premium features but you can decide if you want that afterwards.

The idea that some random company arbitrarily decides it has more journalistic competence than the thousands of actual educated and experienced journalists it aims to assess seems remarkably arrogant to me.

Ground News act as if every media outlet could easily be assigned one of several categories in the political spectrum from left to right. This necessarily implies the misleading assumption that

a) journalism is inherently biased (a view very popular in the US) and that
b) every newspaper offers only a small range of political opinions.

Ground News offer a solution far too simple to an issue far too complex. This is called populism.

Where on the scale of Bernie-Democrat-Center-Republican-MAGA would you put everything published by TAZ or DW? (has to be one value per title, not per author or article)

It is really useful for people whose world view is dominated by a simple categorization scheme (left, center, right), and who would like to remain trapped in it by being educated, day by day, article by article, how to frame each and every bit of news reporting.