Eh. I pulled a 1,000 pound capacity trailer with the single speed version of the trike for 9 years or so. I only had that cart/trailer overloaded maybe 100-150 times. The single speed uses a keyed freewheel adapter for the cog. I never had any problems.
Trike is a traditional two hollow hub rear wheels, left hand wheel free spins, right hand wheel has 3 pins on the axle flange that goes in matching holes in the hollow hub to drive the wheel.
The axle is roughly 30-32 inches long, and 15mm or 17mm diameter, supported by four bearings. The keyed freewheel adapter is a little right of center on the axle, on both the single speed and 7 speed.

The cart/trailer may be rated to carry up to 1400 pounds, but that does not mean I'll have it loaded that heavy. I'm not planning on hauling loads of 16"x16"x1/2" marble floor tiles or a few loads of paving bricks again in the foreseeable future, for example.
I only bought the heavier duty trailer so I would be less likely to overload it.