Superlux HD-669

Sound quality is ok but I would not recommend mixing in these as they are not very flat. Tracking on the other hand is where they shine and I've used them extensively when tracking drums and electric guitars with good results. Also good that the cable is detachable by the ear so that the cable won't break when you step on the cable etc.

The fit on the other hand is way too tight for me and I cant adjust them to fit nicely so I can't use them for longer periods of time. Other people in my studio like them though.

All in all - very nice for tracking but beware if you have a large head.

I bought these for having when recording singers, or any other instrument where you need monitoring but don't want leakage to your mic.

Fits snuggly and are comfortable enough if you don't wear them for prolonged periods.

Sound: Not as clear and airy as the best (and much, much more expensive) headphones out there.
They are perfectly fine for tracking and even mixing if you can't spend the money on monitors or a pair of really good studio headphones. I gave it 5 stars overall as you can see because I think this pair of headphones are absolutely amazing for this price.

Again I want to stress that they got a good grip and press somewhat on your ears, this is good for getting a good isolation but not so good for comfort.

An other point: Good length on the cord, and it is also easily to change it as it has a female jack at the left headphone. You could even clip on a blutooth adapter and have them wireless.

Recommended

Bought them for only monitoring live recording levels at church.
First thing i did was to compare them to my ATH-M50x. Here are my thoughts:

Build quality:
Nothing no praise unfortunately. Manufacturing marks, cheap looking thin cables, cheap-feel plastic, ugly carrying pouch and "leather" headband pads.

Comfort:
These are huge! Pads feel stiff and earcups can only move few degrees to adapt over your ears. But this can be a good thing when you happen to have slightly bigger ears.

About the sound:
I found them very bass heavy, but bass is quite tight and defined. But for my taste, too much bass.
Low-midrange is quite "missing" and what's left is muddy.
Upper-midrange is good! Vocals sound very clean, nice and present through these!
There is a very audible presence boost say, about 5-8kHz range. It gets a little annoying and tiring when listened on high volume for some time.
Unfortunately above these frequencies there is mud again. Highest frequency details, often referred as "air" or "shine", are poorly defined and sound dull.
They are not very sound proof either. Outside bleeds in and otherwise. Wouldn't recommend for tracking.
One more thing, compared to ATH-m50x, they sound "distant". While ATH feels really close, in your face, HD-669 creates "distance" between the the ears and the sound. Can't say if it a good or a bad thing.

Power hungry!
They do need a lots of power to drive them. When plugged straight to smartphone, you cant get anywhere near loud without distortion. But my MacBook Pro preamp did just fine.

FOR THE PRICE I would say amazing sound! Useable for a lots of things, but for serious mixing or everyday music listening, please consider something else. In blind test I would have guessed them in 50-60 euro price range by the sound.

I have roughly around 14 sets of headphones & these are in my top 3
i use them daily (along side the dt 770 & hd25) for editing, mixing & daily listening.

-Pros

+Build Quality is super solid
the removable mini-jack-type connection is a freaking lifesaver, it has saved me & musicians from breaking the cable like +10 times

+Fit
the support wings have metal arms so you can bend them to fit abnormally large or small head sizes

+sound quality is superb
its insane for this price, it easily beats other cans 6x its price. i measure (frequency analyse) all my headphones & there are super small differences in the Left Right hi end (+7K) response which adds depth to the stereo spectrum.
overall response has flat mids, 10db sub boost (20-90hz) & 7dB hi end (5K-12K) boost (with a typical 3.5k cut)

+price
you shouldnt be able to break em, but if you do, its not even a big deal

Cons

-Comfort
the original ear cushions are a good quality but they are a to firm for me so i ll be upgrading them with Brainwavez hm5