It appears the reviews on these 'phones are somewhat uneven. I reviewed the most critical 2021 reviews of this product. (a) inconsistent build quality. (b) dead drivers. (c) small cups. QUESTION - for the novelty aspect, is their sound significantly different from an HD6xx? I have a variety of high/low powered headlamps... Lemme know, eh.
ScubaManLakeHuronI can say the build quality is identical to the HE4xx. I've had no issues. The cups aren't small unless you have enormous ears. I can't speak to the sound difference to 6xx's, but I will say that all planars have a uniqueness to their sound. The way they generate that sub bass doesn't really "hit" like a dynamic driver, it just kinda "snaps" in and out.
Honestly, get them. These things are just unbelievable for the money. The sound differences between them and the 4xx are microscopic (not necessarily better or worse, a hair less treble detail, a hair more bass extension) and every other detail in the build and design is the same.