This is highly open for criticism for it is my subjective opinion...
Regarding the m4: Basic, but i like it and can't say anything else regarding aesthetics. I like the outer edging which will make it easier to grip the monitors to connect the cable to it. The cables fit really tight.
But I prefer it tight
Regarding the m6: I do like the shape. Much better than the protruding pucks of the initial design, which didn't have the class of looks to match the company's higher class sound. I like the screws on the outside and wouldn't mind seeing them larger or more prominent. It's a defining aspect of the aesthetics that can really give the IEM's some character. I like things bold, though. But the outside surface looks a little flat, as if there was something missing to sculpt the final personality into the IEM's design.
I was in the apple store and the black RHA t20's caught my eye hanging against the wall. I found myself looking for Trinity audio, but they're not there... yet