I ordered a medium since that's my best-suited waist size. It fits well around the hips, but it's exceedingly tight around the legs. I find that when I bend my legs, it becomes uncomfortably tight around the back of my knees.
Unlike other leggings made from synthetics (lycra, etc), these do not stretch very much. These are presumably designed for when warmth is more important than flexibility. Having said that, the merino wool layer is very thin; I think these are only marginally warmer than my more-flexible running tights.
Finally, quite a lot of stitches are coming loose (both at points where it's likely that I over stretched them, and also at places where that's unlikely).
I'm going to wear them as sleeping-bag pyjamas when I go camping, but I probably won't wear them for hiking.
Still fond of Helly Hansen in general, but wouldn't buy these particular tights again.