The Cloudultra 3 is On's shoe for the longest trail days: max cushioning from dual-density Helion HF hyper foam, with a nylon Speedboard added for stability and support once fatigue starts making decisions for you. The positioning is control and efficiency over technical ground at ultra distance, not short-course speed.
It suits you for ultra races and the mountain training blocks behind them — hours-long efforts where the shoe's job is to keep your foot working honestly on rough terrain.
It is not nimble, and at 295 g it is not trying to be. For faster, shorter trail work On's lighter models exist; this one is bought by the hour, not the kilometre.