I have used AKG's before, and I was in need of a cheap set of phones to replace my busted Sennheisers that I use for work, so price was a factor. I looked at the reviews on Amazon before purchase, and I have to say I'm delighted with the product.
I've had them for a week or so, and so here are my first impressions....
1. Initial sound out of the box was much larger than my previous headphones, and a little tinny compared, but the bass was solid, and the sound was still clear.
2. I listen to rock/metal so they have had a good test now, and they have warmed up nicely, the tinny sound has abated, and there is a lovely wide sound with all the instruments and vocals heard clearly.
3. I use these on my HTC One, and again they provide a great sound if you're looking to use them on the move.
4. I also use these at home for gaming (Counter Strike) and they provide a good soundscape for games - not perfect, but it's not what they are designed for, but do a good job nonetheless!
Overall, I would say these are definitely worth the 5 stars, the price is amazing, the build quality is pretty good (a bit plasticy, but what do you expect for £20?) and they sound solid all round.