This is a terrific jacket.
Everyone has a slightly different fit - I'm quite tall and slim and some brands just don't fit me that well. It just so happens that Rab products fit me perfectly.
I currently own a Rab Baltoro Alpine windstopper, which I love. It comes walking, climbing, and to the beach with me. But in preparation for some more serious adventures, I wanted something as a mid-layer to wear underneath my current jacket but over my base-layer.
This was the perfect solution. It's a bit thicker than a micro-fleece so doesn't squash down quiet as small, but is still fairly compact and light.
Bonus points, however, for breathability. I usually run quite warm and so am very cautious of over-heating. This fleece is brilliant, I feel suitably ventilated, even when exerting myself. It's comfortable to wear climbing, fits a harness perfectly and can deal with the change in pace from a strenuous multi-pitch to standing around for 20 minutes on a belay.
To top it off, it looks good. It's a sexy grey, a snug fit, and goes perfectly over a t-shirt for a trip down the pub, or for a bike ride round the park.