I have not yet used the Iron Ultra-Tow 5x8 Aluminum trailer, but I may have a build in my sights ... Anyways ...
Why exactly are you concerned that the frame is constructed of aluminum? If it's capable of carrying 1715 pounds (assuming the manufacturer did its due diligence), that's what matters. Since most teardrops are relatively lightweight (particularly in relation to a 1715-lb trailer), I don't think you'll encounter any structural problems just driving down the road. And yes, aluminum flexes more, but the shell of your teardrop should be responsible for most the rigidity.
And you never have to worry about rust

Again, I'm just arm-chair speculating ... but I'd go with it. Seems like a good way to save weight. Any one else see things differently?