Got this jacket (XS size) in the mail today and was a bit disappointed with the colour and fit. The actual colour is not as green as in the image. Rather it's more like a pale pastal light green. A bit too pale for me. The sleeves are quite long too (although I believe this might be a design feature and intentional). The length of the body is also quite long (the waist sits below my hip bone). Also the cut is slightly loose. But I am 147cm tall (short) and 46kg. So I probably fall below average for small!
I also bought the Houdini Transit Lounge Hoody which I love. The colour is true to life. This product might have the same cut as the Power Hoody but it seems to be more slim fitting. It could be that the material is lighter/ thinner. I love the button detail and hood design too!
These two products from Houdini give me the impression that their sizing is slightly on the larger size. So if you generally buy XS in other brands, like me, then I would be hesitant to buy a Houdini product in XS because it will most likely be less fitted then what you're used to.
I also bought a Marmot Power stretch hoody (in blue). Which is totally ace! I love this jacket and put it on immediately. The colour in the photo is true to life. Also, the fit is better than the Houdini products. The XS is ideal for me. It sits at my hip bone and the arm length is right. It might be that Marmot have a slightly different sizing system that fits my body shape.