Available again

Available again.

@DrDave

Why not their version of HD650?

I tried all of the Massdrop xx phones and they were all good cans and a good deal. There are subtle differences which I identify as thickness and transparency. None of the ones I tried had what I would call a good treble--they weren't bad, but not great, either. However, they all could be modded fairly easily to produce a good treble and there's lots of info online about how to get the tweak you want.
I personally slightly prefer the stock 600 to the stock 650, so factor that in, but, in any case, the fact that the Massdrop versions are relatively inexpensive and you can tweak them is a pretty nice set of features.
Currently using the 6xx because it is very revealing of audio edits. That's not so great for easy listening because, well, you hear the audio edits which is annoying. The 58x is a little better for easy listening. Out of the box, the 6xx is a bit thick in the treble and slightly covered, but it can be modded.