I have used this a few times now. It is reasonable sized, but is a little shapeless. It is quite thick, but serves my purpose for hiking. The sleeves are cuffed which is good. It seems to wash OK.
However, the neck loses it's shape and stretches open. For it to be 100%, the neck should have some elasticized cotton or spandex to keep it tight to the neck. Like many cheap T-Shirts, it does not hold shape., except it was not that cheap.
For an SPF shirt, it should stay closed and not expose more neck area.