I have an old trailex; the style with the center beam/tongue that only runs to the front cross-beam and is supported by two additional beams that meet up with the center beam at 45 degrees. The only complaint that I have is that the trailer tends to wag behind me a little as the unsupported portion of the tongue flexes back and forth. Also, the mast stand sits in the center of this unsupported section (between the coupler and the point where the diagonal support beams mean the tongue) and as it sways back and forth in the turbulent air behind my Jeep it twists the tongue repeatedly. I worry about fatigue in the aluminum so I keep an eye out for cracks.
I have a feeling that the trailex on the fist page of this thread would suffer from twisting and waging even more as it has a longer stretch of unsupported tongue. An ideal design in my opinion would be to add diagonal supports from the front corners of the frame all the way to the coupler, and to add a cross brace where the mast stand is attached. Another option would be to stick with the design in that picture but replace the center beam with one made of a more rigid material like galvanized steel while leaving the rest of the trailer aluminum for weight savings. It would be one heavier beam vs. adding additional aluminum beams. At least with the diagonal beams you would have a decent area to mount a box at the front of the trailer for storage.

As far as hills go... I don't have problem. My Jeep produces so much drag already its pretty hard to notice any more. Crosswinds are another issue though....
(and those power lines are plenty far away... no worries)