Yes, we have, and to be honest it didn't make any difference, she still scratched and rubbed like mad. This was tried on one of our mares with severe SI. We got a Horsewear Sweet Itch Hoody Vamoose - not rubbed or been bitten once, and this is normally a terribly itchy horse, who is never not seen rubbing or scratching.
If you're planning on trying it, you ideally should start bathing them with it in Feb. so now would be too late if they're already itching.