I have several solid fabric (not mesh) merino base layers too. The course mesh weave itself seems to offer this property of 'range extension', beyond what merino can do along these lines by itself.

It's not night and day, but it IS noticeable to me. I think the mesh helps keep your skin a little drier, and if the next layer beyond the mesh gets a bit damp, it's not in direct contact with your skin, limiting the heat conduction problem of a wet baselayer. The overall problem of sweat and freeze cycle of those of us riding in mountainous terrain is lessened.