I tried a friend's SE215s before I bought these and they were literally the best headphones I'd tried, especially for just how much noise they cancelled out. I opted for the SE425s as they were within my price range and I wasn't and remain not disappointed. Despite not having 'noise-cancelling' built in, the fit is incredibly snug and they come with a range of various tips so you can choose whichever option you feel most comfortable with.
They do get a bit of getting used to in terms of comfort, purely because most other 'normal' headphones don't go into the ear as much as these do, without buying a set of mouldies, however the SE425s also have a really useful tightening slider which means they remain firmly in place, exactly how you want them to be.
A really great set of headphones soundwise as well, the dual drivers provide well enough pump for the bass, you don't need to turn up the volume very much at all. And let's face it, who really needs more than two drivers?
I'd recommend them for anyone looking to buy a pair of £200 in-ear monitors or even general headphones. I tried some Atomic Floyd headphones the other day (also around £200) and they were shocking for the price - great packaging, but a poor sound quality, they didn't stay in the ear and a shoddy cable. The SE425s have a really durable cable as well which doesn't look set to break anytime soon.
Great headphones basically! Just make sure you turn your phone to silent when walking around or there's absolutely no chance you'll hear it…!