I have one. I liked not being confined by the length of a cord. It stays hot for 30-40 minutes. I stopped using it because I think it was smashing my hair and making the tangles worse. I still use it when I go out of town, though.
I saw this cap a while ago and wanted to get one but never did. I think I'm going to give it a try because I don't always enjoy being confined to one spot when I have to deep condition my hair.