I bought one of these shirts about two years ago from the Bourke Street store it's had a lot of use this year in a fairly bleak Puckapunyal winter worn as a base layer (noting I spend most of my time in an office), I'm sure with addition of a merino base layer it would be very effective as a mid layer garment.
I have found that it provides very good warmth for its weight and is not excessively heavy when wet.
Two points I would make - make sure you check the size; I purchased the XXL although I usually wear X - XL tops (I take a 95R DPCU shirt) and this provides a good fit although the sleeves are a bit long (I simply fold back the cuffs)..
Also as this is fairly pricey(which I was happy to pay for an Australian made piece of clothing) take care of it when packing it away. I suggest placing it in an airtight plastic bag with mothballs as I've had other (granted much cheaper) wool products end up as silverfish fodder. The downside is you might smell like granny but at least your shirt won't be perforated.
Overall a very good item of clothing.