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They're tricky to fit and once in, they can amplify the sound of head movements and noises when you knock the cable.
From my experinence with the CX300's...
I belive that depends on how well you know your own ears. Since buying these I have discovered the inner part of my ear points to the back of my head rather than as I thought, to the center/front. When you get used to them they are fine.
The do definitely have increased movement noise from the cable, Ones voice also sounds different. Very similar to having your head under water.. due to the slightly increased air pressure when you insert them.
They do have much louder bass, but its easly adjustable by pulling them out a little, the small adaptors fit me best and dont fall out.
edit: from FindMemory they are £4.32. I have never used amazon before.. are the other companys that sell though amazon good and reliable?