I had two different models and rode a ton of off-road with them both. The first was an inexpensive model I got at Target. Paid $75, used for 4 years and sold on eBay for $60. Second was a Burley Piccolo. Bought it at a garage sale locally for $75, used it for 4 years and sold it for $350+ on eBay.
Both had their + and -.
Cheap one folded down for easy transport, but was really heavy and cheaply made with a heavy steel frame, steel wheel, BMX freewheel that didn't work, steel handlebars, and steel seat post. The clamp system required a bracket to be mounted on the seat post and pivoted on a plastic bushing. The plastic bushing would break and work out from under the clamp, causing the trailer to become unstable. Different sized bushings were required for different seat posts. The frame was also bigger, so wasn't as usable for the kids as early in their growth.
Burley model was lighter, had gears, was more adjustable, had chro-moly frame, alloy wheel, alloy bars, alloy seat post, and gears. The seat and handlebar adjustments were easy to make. Lower frame allowed for better stand over and let the kids start on it younger. Didn't hurt to have gears. When younger, the kids did not use them, but as they got bigger, they started learning with them. The attachment system, however, required a rear rack to be mounted to the bike. It was very safe, secure, and stable, and the pivot was smooth, operating on headset bearings. This required a dedicated trailer pulling bike.
Overall the Burley was the best unit, but if I had it to do over again, I would look for something with a quick release latch mechanism that could easily be moved between my wife's bikes and my bikes. I would still want it to be lightweight and decent quality and collapsible.