A friend of mine owns one. Graded dirt roads like forest roads you're fine. True 4x4 off road trails like pictured below, forget it. I think it would rattle apart. They are neat trailers. Just depends on the terrain you want to spend time on.
I'll give some examples:
White Rim Trail Moab - No
Lockhart Basin, UT - NO that's what is pictured
El Camino Del Diablo - probably
Mohave Road - Maybe would have to go very slow in sections
Pretty much anything considered a trail vs a dirt road forget it.
Plenty of dealers around the country. Go check one out if you haven't already.
The bigger tires help but I just don't think the rest of the trailer is built to take the abuse.
The Backcountry Discovery Routes - easy sections yes any of the higher rated which are easy with a true off-road trailer - No