Great sun protection!
First, for sizing info, I am 5ft1, 106lbs and I got the XS. It's fits perfectly for my taste; loose but not extremely baggy. I got the Arctic Blue and the Columbia Blue (pictured).
As for performance, I am overall very happy with these shirts. I believe they are as light and as breathable as a full a sun-protecting long sleeve shirt can be. In particular, I have ran in them during 85F degree weather and they did the job for me. I may have heated up a little bit more than if I were just wearing a sports bra, say, but they still felt breathable and, especially for longer runs, the sun-protection kept me cooler by the end of my run.
The only slight con I could think of is that they are not very odour-resistant, but I think that is to be expected from such materials. Definitely not a deal-breaker for me.