I do not own a fifth wheel, but I drive commercial carriages galore, and most of them are 5th wheel. I love them, but they are what I started on, so I may be biased. I still think it feels funny to pivot a horse in a two wheeled cart where I am still facing the horse when he gets 80 degrees around. They are more dangerous than a two wheeled cart, as they can tip over, but a short based wagon with an experienced driver and experienced horse should be fine. I, personally, prefer a 4-wheeled carriage as I think they make for a much smoother ride and less bounce on the horse when going cross country (especially when you drive a floaty trotting Arabian, lol). I would only ever consider a fifth wheel when it comes to a 4-wheeled vehicle.
I have known cut unders that are not fifth wheel, we call them "reach" carriages, no clue where the term comes from, but the warning I got was you NEVER turn more than 45 degrees in it or it will break. I never tested the truth to that, just kept our turns wide. Always made me nervous to drive them, so I massively prefer a fifth wheel. We have a big 25 person wagon with a fifth wheel and due to it's length (and the number of people in it moving around and rocking it) it was considered fairly easy to tip over, so another always stay within 45 degrees of center wagon. I never had it tip, but I could feel it wobble when we got past that point. I've had a short based fifth wheel get well beyond the 90 degree point (horse running in reverse) and although it made me nervous, it never actually felt like it was going to tip.