I lift two hives at a time with my "very generic" easy loader boom system I made. Im sure their system could do it.
I may be wrong here, but a set of double deeps probably don't weigh over 275 lbs. If both top deeps were full of honey that would be around 180 lbs. The two hive pallet I make is probably 15-20 lbs at the most, not really sure. Now if both bottom deeps were packed with honey that would send it over the limit, but ive never had the bottom deep packed with honey at a time where I needed to move them, actually I don't think Ive ever had the bottom deeps packed with honey period.
I don't think I would worry about moving doubles with that Ezy Loader you have a chance to buy at a very good deal!!