If a "back-loaded horn" is like a folded horn, or any type of horn, he is using a close to logarithmic curved horn to magnify the bass, as does a megaphone. Klipsch did the with their horns and folded horns for years. Twelve watts would create enough bass to shake your home, with the Klipsch. Whether this guys is using the same principle I cannot tell you. If he is it might work.
Speaker design is the last outpost of voodoo and black magic in audio. No, it is the biggest. There is still lots of snake oil in this business.
Later: It looks like this is a very simple single fold horn. I would prepare to be underwhelmed. I heard some of these simple horns about 40 years ago and was underwhelmed. Maybe the bass was truer; maybe it just wasn't there. YMMV