Very light insulation, but perfect for just the right conditions
The irony of this fleece is that the conditions that make it useful are not life-threatening, and a generally nothing more than a bit uncomfortable. Its a great layering piece, but its best use is just throwing it over a t-shirt or over your shoulder for a quick hike or a night out when you know that you might be a little chilly later.
It breathes very well, and is a great choice for high energy activities when you might start out chilly but know you'll warm up. The fit is great, athletic as always, since its Arcteryx. Though, that also means its a little pricey.
I'm not sure I've seen many fleeces that are this lightweight and fill this niche. Its not for everyone, but when you find the sweet spot for this fleece you'll keep coming back to it for just that right amount of warmth.