I have one and have mixed feelings. Ours is pretty large, with 2 queens, a storage box in front, a popout, heat and toilet. I think I bought it mostly to entice the wife into camping, and she and the kids do like it, but the kids like sleeping in a tent just as well and she probably does not come any more often that she would have anyway.
As far as the benefits, it is very easy and safe to tow compared to a conventional trailer of equivalent size. It is very roomy. I have not had any condensation problems, and the heater does work nicely. With all of the windows, it is much less stuffy than a conventional trailer during the summer. It is pretty easy to set up; it takes me about half an hour by myself, or about 15 minutes if the wife helps. I especially like how easy it is to backup into a campsite, and I have been able to get it into places that I never could have with a regular trailer.
The downsides include that it is fundamentally a weak design as the walls don’t have a ceiling to hold them in the proper alignment. The canvas, while pretty durable, is prone to ripping, but if you were absurdly careful you could probably avoid that. There is of course little storage room, but that is part of what makes it feel roomy.
Like any camp trailer, it is not really built well enough for rough roads. The structural weakness probably makes it worse than most.
My lift system just failed last weekend, so I am down on tent trailers more than usual. I really wish I hadn’t bought the thing and just stuck with a tent. I would rather have a tent trailer than a camp trailer of equivalent size, but a nice tent is in a lot of ways easier than either, and certainly a lot cheaper. While the bed in my trailer is nicer than a simple air mattress, I could have bought a huge tent and a terrific camp mattress for a fraction of the price.