I've heard the Helene DAC in a really great system and it was excellent. Really open and natural sounding. Prior to that I believe they were using a more expensive MSB converter which I felt was not as good as the Helene (system owner agreed with me).
I've also experienced their more expensive Kassandra DAC, and I didn't care for that one as much. That system was better with the Lampizator they had prior (system owner disagreed with me).
Just goes to show we all have different preferences, and also synergy can be a tricky thing.