As an owner of a dual axle Diamond C Gooseneck with an engineered frame, I can attest to the quality of the trailer over PJ, Sure Trac, Load Trail et al. Is it a worth a $10,000 premium over a triple axle Sure trac?? Only you can decide that.
You wont be giving up any maneuverability, you're just spreading the load out over 3 axles instead of 2. The trailer will pivot on the center axle and the front and rear axle will scrub, so you're not REALLY creating more tire wear, other than it will be more pronounced on the triple axle over the double axle. Id think its a wash, but I have never owned a triple axle. I would personally still be inclined towards 2 axles instead of 3.
Diamond C customer support seems to be top notch as well. When I got my trailer home and went to grease the equalizer pins on the suspension, one of them wouldn't take grease. They sent me 2 new ones immediately.
I would also recommend the Shocker... once you dial in the air pressure for given loads, it pulls so much smoother.