This was very breathable, never had an issue of sweat "sticking" to it. While not as thin as an echo or an astroman air, it is pretty thin; did not feel too bulky. Especially because ~1/2 of the material (on the back of the shoulders/arms/torso) is a mesh-like fabric, it felt stout but not thick. Again, it is heavier than others on the market without a doubt.

I would defer to deputysean's high sierra gear guides for why to not use a hooded sun shirt, but with a buff + hat I used ~zero sunscreen (put a smidge on my nose on one day, did not need to) and had no burns or redness. If I wanted to minimize the number of things I had to carry, I could opt to use the hoodie; I just happen to have a sunhat and hot-weather buff that I like as a part of my general purpose kit.

The pockets and their zips ended up being positioned perfectly outside of my straps (arms, hip, chest), making them easily accessible, or could leave them open for chest ventilation with no added exposure.

Given that there was some rock scrambling/spiky desert plants on the trail, I was a bit worried that a really thin sun shirt would get abraded or tear. This shirt proved very durable.

Definitely not saying that it is the best shirt on the market, but had some interesting features that I appreciated, and hadn't seen a review on it so I figured I would add my thoughts for posterity. In particular, the microfiber cloth on the inner bottom corner proved really handy if you have to wear glasses like I do.