I picked up a set of these yesterday, so thought I'd throw an impression or two into this thread. I got them for £15, which I consider a steal because I was just probably just going to grab some flats. I briefly considered splashing a little more on the s400's until I saw these.
They're very light, very comfortable, have excellent isolation for an on-the-ear set (the pads really mold to your ears), but I've found they leak a bit - you'll probably get by on public transport, but you'll annoy people if you're sitting in a doctor's waiting room. I read somewhere else that they don't leak - not my experience when I gave them to my girlfriend to try.
My initial impression is that these are a £15 headphone, so I'm quite happy because that's what I paid. So far I've been using them to listen exclusively to Sigur Rós and Sonic Youth, with some very different results. One band leaves me valuing them higher, the other leaves me hardly valuing them at all.
Sigur Rós sound as gorgeous as I could ever hope them to sound through a £15 pair of 'phones. Strings have a lovely open, ringing quality to them. Percussive highs are incredibly crisp (very impressed with these), percussive lows pack a punch on occasion. Vocals are clear enough to pick up some layering not always apparent through different equipment, but they're not quite as pronounced as they can be. The bass is simply alright - it's loud enough, perhaps a little boomy, but also a little muddy. The soundstage is excellent - I really feel like the music is encompassing me and can feel the effect of instruments spread across channels as them positioned around me, which is not bad for a cheap stereo set. I've just been to see Sigur Rós and have been a little upset that at how flat they are recorded compared to live, so to get some depth from a £15 outlay is nice.
Sonic Youth have been an absolute nightmare so far - I prefer my cheap unbranded buds that came with my cheap phone. Sonic Youth can be a bit heavy at almost any range compared to Sigur Rós (who are usually very balanced and neutral). They both have stuff that is similar at the high-concept level, but Sonic Youth have a habit of cranking everything up and go for a raw, aggressive and distorted sound where Sigur Rós choose ethereal. I think Sonic Youth have really exposed the early character of these 'phones. Percussion, as above. Vocals, as above. Bass - muddy to the extreme, very poor pronunciation and it just kind of bleeds into everything. The mids are hideous - compressed and flat. The mids are a bit of a strange one because I can hear things I couldn't on similar priced sets, but they just don't sound distinct. Given that most of Sonic Youth's spatial sounds comes from sweeping walls of guitar noise, the soundstage is non-existent. I realise a lot of folks probably think I've just described Sonic Youth perfectly on any equipment
My first impressions. Please take with pinch of salt (I've only been listening to two bands!):
Beautifully crisp and clear highs - I can't stress how wonderful they are at this price;
Mids with a decent amount of detail that are 'nice' with sparse and relaxed music, but which struggle with busy songs;
Strong, epic bass that collapses into a dirge for bass-heavy music;
For £15, vocals are good. Not chilling or "hair standing up on back of neck" good, but good enough to reveal a lot of the vocals that are often mixed into instruments;
Wonderful acoustic soundstage that's not so wonderful (flat) with amplified instruments.
Not really one for 'burn-in', but I will definitely be back if my impressions change in the near future. I suspect the s650's might be quite good for classical music, so I'll give some of that a go, too. For £15? Totally worth it, but my first impressions are that these are not neutral - your mileage will depend on what you're listening to and, as such, you'll probably be buying these for a specific use.