I wanted to achieve this, and found it worked as described. However, I needed a bit more flexibility. I messaged Alex a "feature request" to be able to select "Where do you want to apply this theme" so I could have the add-on effect all child pages but NOT the parent page. Within hours, he had a new version with the added functionality. Now you can select "This page and all it's children", or "Only this page" or "Only child pages". (Before it was only child pages). AWESOME. Now this is in my opinion a super useful add-on if you need more than one theme on a site. And what more could you ask, especially since it's free!

If you're using a previous version, UNINSTALL it before upgrading! I did this to be safe, but forgot to on one installation, and it broke the site. I had to put the old version back outside of C5 (via C-Panel or FTP) to correct. Also, delete any applied themes first (or you won't be able to with the new version) and then redo them once you've upgraded.