The wording on the XLN site may be unintentionally misleading, at least it was for me. The wording I saw makes it look like Revalver HPse is free for AD owners, and Nectar Elements is free for AK owners. But I was able to download, install and license Nectar Elements even though I own only AD via Sonar X3, so what scook said appears to be true.
I like Nectar Elements, it's a nicely implemented alternative to Sonar's VX-64. I am grateful to XLN Audio (and Izotope, I assume) for offering this.