That quote from Quik Pak as pointed out is biased, but IMHO fatally so.

1) Force vector analysis shows that at least 2/3's the weight of a loaded single wheel trailer is on its own wheel.
2) They argue with a pannier straw man. Did you notice?
3) Balancing the BOB/bike combination has never IIRC been identified as an issue. Most report that they have to look back to see if it's still attached.
4) I supposed it's possible, but I never heard of of a frame actually being broken by a BOB. Worry, yes. But IIRC no reported experience.
5) Attaching a loaded BOB trailer is indeed awkward until you figure out how to do it.

The issues with 2-wheeled trailers is that they have, well, two wheels. If you are hugging the edge of the pavement, one wheel is off the road. And when negotiating potholes three lines have to be considered. Having said that, some experienced tourers really love their Burley Nomads.

One advantage of two-wheeled trailers is that they look like they might contain a baby. Some drivers will give you a wider berth for this reason.