Having worn them a lot riding out in Mallorca in high 20’s and Tuscany, Pyrenees and Alps etc and with a large number of people who also ride regularly across Europe on multi day road rides I can certainly vouch for my opinion on them working very well.
I can’t tell you how it works scientifically, but they do work…
Things like, the mesh creates small pockets of air which means you have areas of skin which are not in contact with material and there is airflow between them. As anyone who knows about layering, you also want to transfer moisture away from the body from one layer to the next to keep you dry.
As I said previously, if you wear a backpack, they will not work as the weight of the back compresses the mesh taking away the airpockets (or something)
I use Craft ones from Wiggle with jerseys made by Howies, Sportful, Ale, Exteondo and they all remain much drier than if I did not wear one.