I took the plunge and went down to Handheldaudio today (The benefits of living in London)
Yes, they are the limited editions. I now have #792 out of 1000.
A quick summary:
If you have the pro 5s you'll recognise the type of sound, but better in all areas. There isn't a night and day difference, more like noon compared to half past 4

But the treble is sweeter, midrange slightly better (so far) and bass stronger. All in all they make music sound more refined (but I don't mean boring: They can still rock, but they sound more effortless).
I haven't tested them on great equipment, only my Archos 500 and my computer. Perhaps the difference between it, the 5 pros and the E4cs will be more apparent with better gear.
I'll be interested to see if they improve with time (I've only used them for about 1 hr) but I am noticing little things I hadn't with the other phones (if I swap the old phones in I can hear the 'new' things, but they aren't as marked as they wear on the 10s)
They are a little harder to drive than my year old 5s, but not excessively so.
Sizewise they are about 7 or so mm longer than the 5s, so relatively big, but they look nice.
I was pleased with the roadie tin and grey carry tin, but was a bit surprised not to get the UE leather case like I did with my 5s. Oh well.
Worth £225? Dunno. Diminishing returns and all that, but then again I wasn't happy to pay £100 odd for the 5s and £130 odd for the E4Cs! As I say, perhaps the difference will be greater with better equipment than mine, but there is a definite difference at the moment.
I'd like to compare them with the Shure E500s. Anyone in London with a pair who wants to spent a little time comparing? If so, get in touch.