The thing with merino is that it's hot. Very hot. I think I just managed to test the New Balance Merino Half Zip Hoody in the maximum possible temperature! It's a very balmy 21°C and it is hot out there. Merino wool may wick away sweat, but only a certain amount can be taken care of before you are running in what feels like a wet sponge.
That being said, this is a winter item of clothing and we are still very much in our “summer”. Being Merino, the fabric is very nice against the skin and is the choice of many sports brands' base layer material. It's a nice fit in general but is by no means a slim fit. So where this top may be fitted for most people, not being slim cut means it won't show off your athletic shape if you are a typically lean runner.
Merino Wool has so many good qualities and there are so many reasons why you should consider wearing activewear made from this material. It has great heat exchange, wicks away sweat, and it is sustainable. More to the point, it is nice and warm in the winter. Some runners in the UK will wear short sleeves right up until ice comes. Maybe you are okay with just a longsleeved t-shirt on. But this merino top is definitely going to keep you snug it as a base layer or an outer layer.
We have taken this top out for several rounds now and it is extremely comfortable. Even though it is not really cold enough to be wearing such a warm layer of clothing at the moment, I haven't felt as hot running in this top as I do in some thick t-shirts. The half zip, however, does seem more like a fashion accessory than something functional for running. It is not low enough if it really is for ventilation and it does flap about. But zipped up I have no problems with it.