Reading through this, several of the pain points here — seeing filter dependencies, testing without reopening the editor, and sharing a complex filter — are exactly what pushed me to build a gramplet of my own, FilterWorkbench.
It takes a different angle from FilterParams: it’s built around the building flow, with helper filters as explicit named stages and a live match count that updates as you add rules. The Test button runs the filter in the person view without closing the builder, which is the “test without the useless wide window” itch from the first post.
I’ve written it up in its own thread if anyone wants a look: Here
Not trying to duplicate FilterParams — more a complementary take on the same problem.