I bought these headphones a year ago now to replace a set of Etymotic ER6s that broke.
My first impressions were that the build quality on these canalphones was much superior- with more heavy-duty wiring than the flimsy wiring of the Etymotics that lead to one headphone breaking.

In use they are great- although as with all canalphones there is a learning curve present in actually fitting them to your ears. They come with an array of differently sized ear-pieces so that you can be assured of the best fit. Be warned that the foam pieces will soak up your ear-wax- leading to complaints from those who ask to borrow them!

The sound quality from my set is great, and the isolation you get from them is also very impressive. I think that the isolation is probably of function of the material that you use as the earpiece, but either way you can easily blot out the background noise on a street or in a train.

I'd really reccomend buying a set of these- I found mine on Play.com for around £25.