If you've seen the pictures and videos you'll know that although they can be registered as trailers and can be towed that they have 2 drawbacks - aerodynamics and weight.
You'll notice in the pictures where the Tiny House company shows them delivering a unit that they use a U-Haul box truck. It's my opinion that part of the reason for the box truck is to deflect air around the trailer while towing. The box truck probably also hauls install-related supplied as well. I suspect any pickup-style tow vehicle will get terribl;e fuel mileage.
You've seen the construction of the trailers. Many have nice finish grade tongue and grove walls and ceilings. They are built more like S&B houses. I would expect that they are very sturdy and will have a long life. In comparison an RV is built more like tooth picks and styrofoam.