That is a loaded question, sorry I haven't towed or owned such a unit, I have however towed just about every type of trailer out there, and every time I've had an issue with unstable highway towing it has been due to unbalanced loading, (too much weight in front of or behind the axel(s). I have had to pull over and reload the trailers. It can be very scary to find yourself towing a rig that develops a sway at highway speeds, this can whip your trailer and TV around, and you will do your self a great favour by slowing down smoothly, (don't slam on your brakes or hit your trailer brakes hard with the hand controller) and pulling over to find out what is wrong.
I have also seen others have issues trying to go way too fast, or towing with a very short wheelbase vehicle. I have witnessed jackknives in front of and beside me as well as a pop up that turned on it's side behind a jeep (high CG and short WB) at 75 MPH in the passing lane. That was probably way more about the driver and the speed than the stability of the trailer but i don't think this would have happend at that speed with a tandem axel peterbuilt and a triaxel 53' trailer loaded with lead.
If your dealer won't let you hook up that trailer to your TV and take it for a decent drive down the highway don't buy it from them and find one that will.
If you aren't experienced with towing try to get a friend or family member to go with you on that test drive, and take a turn at the wheel, and give you some tips when you take your turn. That will help you make a decision.
I have found that larger trailers with more axels have more at stake and therefore get built with better suspension, frames, hitches etc, so most of my bad experiences have been with smaller trailers (like pop ups) single axels can be very unruly, But they don't have to be. A sway controller can help and I have used them in the past but I'm not a fan of a tow set up that requires one to tow smoothly, these can fall off in transit and then what are you going to do.
Al, Travelling with wife, daughter 5, son 3, 3/4 tons of 2013 Ram CCLB, five tons of fifth wheel Rockwood 8287SS still showing my kids north america one campground and road trip at a time.