I have actually had Atholl Brose. We had some Scottische-types in the SCA in San Antonio who made it. Local mead was better ;-).
We use an SCA recipe from ca 1988. Very good! Others in the Gaelic society make it from other recipes, usually watery to just so-so. I have yet to encounter a mead that comes close to our Atholl Brose, though if/when I retire I may try.