I would be skeptical of any trailer much heavier than a gooseneck w/ 10k axles built from mill run material. It just doesn't hold up in the long run. They can't build any positive camber into it and eventually it'll be running negative, plus lower tensile material doesn't have the "memory" of higher tensile and once it's sprung it's gonna stay that way. I'd REALLY like to see their slide setup. I mainly want to see how long it is (front to back to see how they spread the load) and how much of the deck is supported. Also, how wide are the main beams? Crossmember spacing?
The potential issue I see if the slide and main beams are narrow a larger machine that's wide and setting out towards the side rail may start to bow the deck. Now if they use a fairly heavy channel for the side rail and the crossmembers are a tight spacing I wouldn't be quite so worried. If there's ever even the slightest chance you'll haul a solid tire forklift you'll want 12" spacing for sure. Those are as bad or worse than a compactor when it comes to punching through a trailer floor.
My concern on the beam width comes from seeing the early sliding axle and even some tilt trailers built with narrow beam centers causing a cantilever affect from the main rail out. Using domex seems strange to me, usually they go to T-1 when upgrading and building a fabricated beam. I had one 13 axle that was domex and it was very "springy" for lack of a better word. Moreso than T-1. They may use domex in high wear areas like the slide to mitigate damage. If so that doesn't do squat for structural integrity.
I see the attraction to that style trailer. There are places it would sure be handy. Even more than just a hydraulic tail. If they can send their "standard" spec sheet to you we can look it over and based on your needs I can offer suggestions to upgrade various things. I'd want a winch on it, key slots in the floor like a rollback, 12 or 15k axles are fine. No matter what I'd want 17.5 tires. I'd really consider something other than electric brakes. They just don't last.
I guess it boils down to your budget and intended use....