The Acoustune that really started it all for us and got Singapore on their feet. The classic red-gold 1551 with copper chamber from 2017 is still valid today in 2019, and it remains one of our top sellers for the ease of presentation on liquid smooth tone simulating listening in an acoustic chamber. It's also when Zepp Crew quickly learnt the word called a "Myrinx driver", which we won't attempt to explain without the supervision of a Japanese engineer.
There aren't many made like these. Hear it if you haven't.