This jacket feels thin, light, and supple. You hardly notice it while walking, and the elastic sleeves and hood fit snugly without flapping. The airy zones allow heat and sweat to escape, so you don't overheat.
It works best when the weather and your exertion constantly change. Think of a trek in the Alps where the wind suddenly blows hard at the top of the ridge, a windy run through the dunes, or a cold start that warms up after an hour. On a long climb, you notice the difference: you take off your sleeves and keep your torso protected without overheating. At the top, in the wind, you put the sleeves back on and stay warm during the descent.
If in doubt, consider the weather you will be running in. The jacket is water-repellent and will keep out a short shower, but for prolonged rain you will need a proper raincoat. It is also not a warm layer, so in cold weather you should wear a long-sleeved shirt or fleece underneath. Because it folds up so small, it fits in almost any trail vest or belt.
In short: an ultralight windbreaker that is also a bodywarmer, for changing conditions.
