Jorge, those receiver classifications make a lot more sense to me than the overly restrictive ones used here. Things like the AR-1780 are not included because they are a few cubic sentimeters too large, but five or ten pounds of ferrite rods, and multi hundred strand wire, that far exceed the size and weight of the radio are OK.
I actually have an AR-1780 as well as a Tecsun 310et and an Eton Satellit Grundig Edition (also likely too large to qualify as an ultralight). The 1780 is the best of the three in reception in a number of ways. And because it DOES have SSB, and a great fine tuning feature, I can listen to things the Tecsun has no chance at and the Satellit is nowhere near stable enough to receive.
I do have one of the FSL antennas. I don't mean to put them down at all. It is wonderful! But I just don't understand sticking to a strict classification of ultralights when something slightly bigger just works better.