If you're familiar with Shure's naming conventions you'll be able to tell that the SE425s are the company's latest dual-driver offering; a model down from the triple-driver SE535s and the successor to the three year old SE420s. Like the SE535s, the SE425s don't have that many differences from their predecessors, but not through any fault on Shure's part - there simply wasn't much that warranted changing.
As such the SE425s party piece is the use of detachable cables. Each earpiece attaches to the wiring with a gold-plated MMCX connector. The benefit of this is twofold: first, should you need to replace the cable or a single earpiece you can do so without having to buy a whole new set of earphones; second the connector lets the earpieces swivel around, helping you to find a good fit.
We might mention, however, that although the modularity of the design is in theory a good thing, the reality is that replacement components are pretty expensive. We found a new cable on sale for just shy of £50 and a single earpiece will set you back about £115 - more than half the price of a new pair of SE425s. Obviously these individual pieces are cheaper than buying a new pair of earphones, but don't go thinking they're an inexpensive solution.
Still, the attachment method is also particularly useful away from replacing a broken set of earphones. The couple of inches of wire before the earpieces are reinforced and the rotatable earpieces stop the cable from becoming tangled when inserting the SE425s. This section gives the rest of the cable - itself reassuringly thick and sturdy - a good degree of support when hanging from your ears, reducing microphonics and ensuring that the earpieces stay securely in place.