Pros: Comfortable. I Can Haz Bass 4 Cheap.
Cons: Needs more power than typical small player offers. Poor stereo imaging. Zero isolation, beware hearing damage.
Packaging, appearance, warranty, euro-nanny knows best:
Mine arrived in the small European packaging box, branded as Pulse clips as well as "Koss high performance on-ear clips". With the clips came the Koss warranty and the euro-nanny-state leaflet on waste disposal. The phones are the silver plastic Koss branded items everyone knows.
The lifetime warranty is valid but irrelevant because shipping costs from UK will exceed the value of the product. But I do very much appreciate a company that has faith in its products and is known to honour the warranty.
Construction, design, materials, euro-nanny isn't done yet:
The slightly odd design works extremely well. With a little careful bending of the plastic-enclosed metal clips I got a good snug fit and no discomfort. I wear spectacles with ultra thin titanium frames and there is no difficulty. With more conventional specs there could be obvious problems.
The silver plastic parts are a blast from the past, looking like cheap stuff I remember from the 1980s. But I don't care. The materials clearly do the job and don't cost much. The cable is unremarkable, 4' long with a straight jack. When I go to plug it in I notice a tiny sticker attached: it's another euro-nanny warning not to dispose of electrical items in household waste. Yes mummy. No mummy. There is a committee in Belgium worried that the first thing a customer will do is cut off the non-detachable cable and throw it in a landfill. I won't do that because I like to listen to some tunes while burning old tires and drunkenly shooting at endangered species in the national park at 2 am.
Everything seems properly assembled and when I press play it works as intended.
Using with portable players:
The Koss KSC75 need much more power than typical budget portable headphones, IEMs or buds. With a player like the Sansa Clip+ you'll probably need to run it at or close to maximum volume which means battery life is reduced. This is especially true for well produced music such as from before the modern loudness war fashion, and any classical music. My iRiver H140 and H340 players put out about a third more voltage than the Clip+ and do a much better job of driving these Koss earphones but unless you're in a quiet environment it might both be not enough and also too much because.....
There isn't any in either direction. If you use these on public transport everyone will hate you. In the street or a noisy workplace you'll hear everything around you and anyone close by will hear your music. The natural thing to do can be to keep raising the volume. This is the road to hearing damage. Compared to using IEMs I find myself running the Koss 'phones at dangerously higher levels and still finding the background noise doesn't let me fully enjoy the music. Beware.
It has some bass, which is a welcome contrast to similarly cheap buds and IEMs. I've listened to some orchestral music, some harpsichord pieces, some choral music, some heavy rock and some bass heavy electronic stuff. The sound is nicely balanced and generally enjoyable. The biggest defect is poor stereo imaging. There is no possibility of imagining oneself being present at the performance. There is no convincing illusion such as I get with a really nice recording and my Shure SE215 or Sennheiser CX 95. With the Koss 'phones the impression of sound is close left, close right and a slightly recessed bit in the middle. Some of this is due to the lack of isolation. For the last few years I've been using IEMs and closed and semi-open headphones. I am really surprised how background noise such as the rumble of traffic from the street below or a kitchen or bathroom extractor fan might not be loud enough to dominate the music but is enough to really kill the dynamics and imaging in a fully open 'phone.
The above might sound overly critical but I'm trying to describe the experience without allowing the price and value to totally colour my opinion. It's true that the Koss KSC75 is still unambiguously better than any bud or IEM included with any device I've ever bought.
Is it worth £10?
Yes, but I might not have bothered if it had been £15 and I definitely wouldn't pay £20 because for £30 I can buy Sennheiser PX 100-II that have much nicer sound, work better with low powered portable devices, are made of nicer materials and come with a carrying pouch. I would also hesitate to recommend these to anyone because the tendency to keep raising the volume to dangerous levels is hard to avoid. Because you can get a better sounding headphone at £30, and better sounding IEMs at less than that, the Koss is running out of selling points and has too many drawbacks. The most attractive feature is probably the clip-on design which is great for runners and people working out and those who won't or can't use IEMs.
It's about 9 pm here, the traffic noise has died down and I'm starting to enjoy the sound much more. And that's why these are hard to recommend as portable 'phones: they only make sense in quiet environments where others won't be disturbed. I expect to mostly use them with my PC because the USB soundcard has enough power to drive them properly and it's good to still be able to hear voices, phones, the doorbell and so on. These are also good to use with a mini system or domestic portable.
As odd as they look. An idea whose time has come and gone. Worth £10 or £15 but not giant killers any more.