I have just got hold of mine today. I got the red-black version and it looks stunning (I like the deep crimson hue a lot)
I'm one of those lucky ones who find the fit not a problem at all - tho I can see why some ppl would struggle with them. Yes the earcups lack real swivel, and that matters when the enclosure is small and the direction of sound projection is important. However, after less than one minute of trying, I got the perfect fit.
The cans are smaller in real life than in the pictures. I dun have my PX200II with me now but I think the earcups of DTX300 are a bit smaller. The cable is nothing to write about, and yes there's no visible strain relief, for a reason (I guess - see below)
Once fitted, the sound is, well, IN-CRE-DI-BLE. Enough emphasis, no?
It is not about extension - I love trebles and the DTX300's treble does roll off, but in a nice way that isn't disturbing at all. The bass is very good quality-wise, not the deepest which is understandable considering its size, but very detailed and reasonably impactful. What really excels, and what really makes it sound incredible, is everything else. The quality all across the spectrum is spectecular, nothing is recessed or brought forward, details are abundant (almost iem level of details). I heard many details that I dun often heard in other cans, most notably the T50P. Every single instrument I heard so far sounds almost identical to the real thing itself, and layering is so good that busy orchestral passages sound absolutely convincing and concert-hall like. The presentation is generally airy, and if you're after a very focused and hard-hitting sound these may not be for you.
The folding mechanism is smart and when folded it is REAL flat - I can put it in my suit jacket pocket with ease. And the reason for the omission of any visible strain relief, I GUESS by observation, is that it would hinder the folding mechanism. You'd understand what I'm talking about when you see the cans folded yourself.
Frankly speaking I expect this to be another Chinese OEM products (no discrimination here - some of these OEM products bring shame to the big names in the industry) but no it isn't. It is a quality product at an insanely low price. I listen to classical music the most, pop and jazz follows, and for these genres I'd pick the DTX300 over the T50P (which I still have with me) anyday for details, balance and soundstaging. I suspect the T50P would do better for rock or metal, though I haven't tried.
And, to those who cares, they're made in China. Hence the price I believe.