My gelding as a 3yr old was dry as can be in the middle of the desert summer. Pretty scary when they are doing the heat stress deal. Panting like a freight train, standing in the shade in their stall, dry as a bone.
He has been on One AC for the last two years and it is GREAT. He stays on year round. As a matter of fact I was thrilled last evening (sorry East coasters, it was 85 yesterday) to go and ride after work and there he was standing in the sun in his stall with a little sweat all over, but not stressed. Rode and had a good sweat.
Call me a believer. I get mine through a vet. It is about $25.00 a packet, lasts I don’t know a month or more.