Personally, I see no advantage to them other than them being cute and the residential sized appliances. Unless your a commercial hauler, you will have to hire someone to move it. The interior square footage is still going to be a max of 400 SF as in the largest 5h wheels. A 5th wheel of the same interior size has a lot of built in cabinets and storage underneath the floor of the trailer. It can be moved by anyone with a decent sized truck in any campground.
Be very sure about purchasing one. They're not as easy to resell as a 5th wheel.