The Cascadia is the trail shoe Brooks has been iterating for twenty years, and the 19 is the general-purpose version of it: balanced cushioning at a 6 mm drop, a platform that adapts to whatever you are standing on, and an outsole tuned for wet rock as much as dry.
It suits mixed terrain — the run that starts on a fire road, climbs something technical, and comes back on gravel. It is stable enough to carry a pack and to hike the steep sections, which is why it turns up on so many feet at trail races.
It is not soft and it is not fast. At around 300 g there are lighter shoes for short trail efforts, and if you want the ground to vanish underneath you on an ultra, the Caldera does that job better.