I have about 150 miles on my new ActionBent Partner-II trailer, and it has performed beautifully.
http://www.actionbent.com/twtrailer2.html
I bought two skewers, one for my RANS V2 and another for my Specialized Hardrock. Most of those miles were on the 'bent, but about 25 miles were on dirt roads with the MTB.
The trailer rails fold down for shipping or storage. The only assembly required was to install the 16" wheels, each held on with an allen bolt (wrench provided), flip up the side rails and secure with a clevis pin, install the hitch with another clevis pin, and pump up the tires. Within 15-20 minutes, the trailer was out of the shipping box and connected to the MTB including the time to install the skewer on the bike.
The trailer appears to be well-made. It's powder-coated aluminum. The welds look good if a little heavy handed on one on the top rail.
The trailer comes with a large yellow/black bag which can be used in the trailer for cargo or used as a storage bag for the trailer when it is knocked down. The bolts that secure the side rails are installed so the bolt threads are exposed inside the trailer. This quickly wore two small holes in the bag. I reversed the bolts so the nut and exposed threads are on the outside of the trailer. The holes in the bag were easily patched with duct tape which, using motorcycle racing logic, might make the trailer go faster.
The only other short-coming I found was the flag. It mounts on the rear of the trailer with two small sheet metal screws. It lasted about 3 miles before the thin metal holder fatigued and broke off. I mounted another old flag I had on the left axle allen bolt, and secured it to the side rail with two hose clamps.
The trailer tracks absolutely straight and true. You quickly forget it is back there. Even when a trailer wheel falls off the shoulder or tracks in a rut, it doesn't tend to adversely steer the bike. The hitch is very secure and relatively quiet even off-road.
The longest trip so far was to my RC flying field, a 36 mile round trip, hauling 35 pounds of airplanes and support equipment. The trailer has a max. payload of 77 pounds. The trailer could handle it, but I don't think I could struggle up the local hills with it. The trailer will also be used for grocery trips and work trips to the local citrus orchard I manage twice a week for a local university.
I'm very happy with the purchase, and plan to buy another one as a platform for the mini-teardrop trailer I eventually want to build to carry my RC planes in style.
Eric