Summary: First of all, I don't think we should be comparing these to anything else but in ear monitors (IEMs), and generally in the price range. However, my only experience is with Sure SE 110s that I used for over 5 years. Those were about $99, and I got the 425s for about $270. I've now had them for about four months, and have gone through the slightly disappointed stage which seems to occur for a lot of people with a lot of headphones.
Pros: Balance, imaging, speed from top to bottom, mids
Summary: These are my second pair of Shure IEMs. I had enjoyed the SE210s for a long time before taking the plunge on these. Since these are meant to be worn up only and the cable rotates freely where it attaches to the monitor, it took some getting used to the new cable design. Sound quality is definitely leaps and bounds above the SE210s. The bass is IMO much more substantial on the 425s but very fitting to the music I listen to (all shades of rock).
Pros: New modular cable design feels very solid and well executed, relatively flat sound signature, Bass is present but not obtrusive.
Summary: These are great with comply tips. They look a bit flimsy build quality wise, and a couple of people on amazon have broken off the stems, while replacing the tips - which is a bit of a worry if you buy them used as I did.
The bass is nice and deep but not boomy, but the mids are relatively emphasized and the highs are somewhat recessed (again relatively). This makes them sound somewhat thick and congested compared to say SM3v1/2 or UM mage or aero.
Pros: inexpensive and great mids and deep bass without the usual bass hump. work ok with higher impedance amps
Cons: strange build quality, comfort and sound sig is not as refined as higher end iems.
Summary: I bought these at an online music store for a price much lower than elsewhere. This is my 3rd pair of Shure In ear monitors. The first pair where E2's which broke the tip when replacing the foam cushion, I tried to repair them but they lacked bass after this. The second pair where E310 in black, I loved these but unfortunately left them on a plane.
Pros: Neutral correct sound, extremely deep bass when fitted properly
Cons: More difficult to fit correctly than previous Shure IEM, neutral sound might not be liked by the average loudness and boom bass lover
I got mine open-box off of ebay for 249.99 compared to other prices of 299.99. Couldn't tell the box was opened.
My other and only "high end" headphone was the bass heavy Turbines. Initially, I was disappointed by the 425's as they were really flat and lacked that bass punch.
My friend suggested I burn them in, though I doubt it would do any difference.
Pros: Flat sound, over ear design, eartips hard to get off
Cons: Eartips hard to get off, hard for audio newbies to put on
Summary: I was looking at some high-end in-ear monitors when I stumbled upon these, I directly pre-ordered them for 235 euro, only going by what I heard about the SE420s and having no idea what to expect.
The design is great and very intuitive. When selecting the right tips, the IEMs fit very snugly in your ears. However, they start to get uncomfortable to me after an hour or so.
Pros: Very honest sound signature, great design and isolation, very comfortable,
Cons: No artificial enhancements that make for 'exiting' sound
Summary: I got my pairs (plural) because my last pair of tried and trusty EC-4s bit the dust.. losing the left channel as they tend to do over 3 or 4 years. In the past, I'd send $100 dollars and the EC-4s to Shure, who'd fix them and send them back. Good to go.
Unfortunately, Shure has end-of-lifed the EC-4s. Boo! So rather than fixing them, they replaced them with two brand new pairs of SE425's-- right off the store shelves.
Pros: Great sound, Great brand and customer service