I ride with a suspended single wheel trailer made by Tout Terrain. It attaches to the seat post with an articulated hinge. One big advantage over trailers that attach to the rear axle is that I can turn on a dime. I don't much consider the weight other than what the manufacturers maximum capacity is since I use an electric motor to help pull it. Like you guessed it can make the bike lean when the mass isn't moving. A center-stand, I am hoping, will let me stop, drop the stand and jump off with a camera. The trailer has a built-in stand that keeps it rock steady when standing on its own. Someone mentioned the mass riding high would be less stable and is correct. There are two setting one low (roads) and one high (off road/single track). I was following a rider with a two-wheeled trailer that almost lost control when an inside wheel grabbed a rock and hopped up into the air. He veered to the left where traffic could easily have been. I guess stability equals speed + surface. I would guess that two wheels would support more weight if it were being used for daily cargo run. It is easy to forget it's there at times and that is when physics decides to remind you, road surface, the coefficient of friction (COE), inertia, gravity, even the size and moisture content of an unfortunately placed cowpie can teach a bitter lesson. The picture below is before I tore one of the Salsa Anything bags off of her. I guess that is the one disadvantage, because of the seat post connection she doesn't track exactly when the back tire does unless going straight. There is a learning curve but given enough time physics will show you what you can't do. My dream is to be able to mount a motor designed only for energy recapture (hopefully Vastly improving our current ability) when descending. Pull a separate lever, engaging the drive, slowing the descent and recapturing the energy as electricity, and saving brake pads!. Or even more far fetched... generating power when stopped by mounting a dynamo hub, turning the wheel axle 90 degs. (single swing arm so this would be easy), and attaching small portable verticle generator blades. Let it spin all night as you sleep tight.

Wait, there is another disadvantage, it doesn't use the same size wheel as my bike. Meaning additional tube/tire, spokes etc. for repairs. That is something I need to look into modifying.