NOT GOOD> I got my 4xx. It had a buzzing sound on the right cup, as if something was loose. Wanted to replace. Massdrop told me to send an email to a gmail address (head.direct.customerservice at gmail dot com). It does not even have HIFIMAN domain (even though HIFIMAN has a @hifiman.com domain in their customer service email).
Now I will have to send it back. I guess I also have to pay for it. The given email responded: send us the headphones, we will send you a new one back once we get the one you sent.
Massdrop mentioned that it is under warranty. Defective products when they first arrive should not be covered with "warranty". It did not break down after use; it was already not working properly when I got it. As a metaphor, this is the same as Massdrop not sending the unit, and telling me to go pay to UPS for not sending anything, and then me waiting for a while for the product to be sent.
My friend mentioned me do not buy from massdrop. I did not listen to him. Then he said "I told you".