The Double Dragon loop is a useful loop to know.
( To
invert the understatement of the millenium
"The bowline is a useful knot to know" (1), into an overstatement

)
The Double Dragon loop is a doubled form of one "Tugboat loop", relative to the
so-called Tugboat "bowline" , or the
so-called flying "bowline". ( If I had said simply : "of the Tugboat bowline" or : "of the flying bowline", it would have been an indication that I
"see" things where nobody else does...

, and I am afraid I am not capable of such hallucinations.)
The parent knot, the Perfection loop / Angler s loop (ABoK#1017, ABoK1035) is an excellent end-of-the-line loop, indeed. The structure of all those loops that are relative to the Angler s bend, include a hitch, but not a collar. The Double Dragon is a nessesary improvement to the less secure form of the
so-called Tugboat bowline.
1)
http://www.layhands.com/knots/Knots_SingleLoops.htm