FWIW, Echo1 acts as a “VAR” for almost all the Jing Gong/Goldenbow guns they make, plus some from Kart and A&K.
By that I mean Echo1 supposedly tweaks the guns for reliability and to eliminate OOTB failures, re-packages them, and adds their value-add warranty as incentive.
TSD is doing the same thing with SRC products, but out in the open and not as much "under wraps" as does Echo1.
Anyway, on to your question on A&K vs. Echo1…
I have a JG (non-Echo1-boxed version) M4A1 and an A&K “M Series” M733 (basically a short-barreled M4A1).
They are absolutely from two different companies. I could go on and on about the similarities and differances, but that is for another post.