Trailers with a single rear wheel like the BOB put about half of the weight on the rear wheel of the bike and put a lot of torsional constraints on the bike rear wheel+bike rear triangle while trailers with center wheels like the Radical Design, if well loaded put only a small part of the weight on the rear wheel and almost no torsional constraints (the hitch is a ball).

The Bike Friday trailer has its wheels not in the center, so a big part of the load is also on the bike rear wheel (but less than with the BOB) and its wheels are 12" much smaller than the one the Radical Design that rides pretty well and is really lightweight.

But its true that traveling with a trailer has some drawbacks.