I wear them. I have a few from Voler and Craft. The Craft mesh is significantly nicer than Voler in fit and material.
None of them keep me dry in the summer, but I still wear them because I like to unzip halfway and take advantage of the cooling feel since the baselayer is wet.

Baselayers do nothing to keep my jerseys dry. If I sweat, I will sweat and it wont magically stay at the baselayer level. I wear clothing that is next to my body for moisture transfer blah blah yada yada, but the technical BS is just that for me- BS. In the end it doesnt keep me cool or dry.
I dont think it makes me measurably warmer though.