Rating: 4 / 5
This shirt fits my thin frame and longish arms (size L). I've worn it about 100 days (50 hiking, 50 in town) and it shows no signs of wear. I can wear it 10 days in a row in the mountains without it smelling. The zipper helps for thermoregulation.
In my opinion, this is just the right weight of fabric for the product. Something thinner will wear through more quickly, and something heavier will provide less insulation per ounce than synthetic jackets.
I am not quite as enthusiastic about the Mondo Zip as I used to be. I have found PolarDry to be a significantly warmer layer at less weight and less cost. I don't think I will take the Mondo Zip hiking again because there are slightly better combinations for me, such as:
Icebreaker 140 Tech T
Marmot PolarDry long-sleeve shirt
CAMP Magic anorak
I'm always carrying a short-sleeve shirt as it is, so having that AND the Mondo Zip seems redundant, because the Mondo Zip, as all Merino wool, shines as a baselayer where it doesn't smell.
That said, I wear the Mondo Zip all the time (well, almost) in town and love it.