Pros: Highly portable, replaceable cables, great packaging
Cons: Considerably fragile, due to a lot of moving parts. Sound is a bit muddied
I bought these headphones as a replacement for my (still working) PortaPro, because I needed a nice portable headphone that folded into a neat flat shape. After a bit of reading, I decided to pickup these headphones, and while I wasn't expecting much from them in terms of sound quality, there were other aspects of this headphone that made it worth the purchase for me.
I cannot overstate how much I love the portability aspect of the AKG K450. When moving around, I'm usually carrying with me a Knomo sleeve bag made for the 13" Macbook Air, and with the way these headphones fold, they are about as thick as a notebook.
They are also packaged with a nice carrying case, that is considerably thicker than what the headphones occupy without it, but help it very secured even during long-distance travels, and they come with two cables, a longer and a shorter one, both of which are very thin, but seem sturdy enough to withstand some degree of "punishment". Even though the cables have a proprietary plastic hook that helps keep the cable secured to the headphone, if they happen to break, you can replace them with any 2.5mm to 3.5mm as long as the 2.5mm is thin enough to fit in, and they hold on well enough.
The isolation is fairly good, giving you most of the musical detail you expect from a closed-headphone without completely omitting the sounds of your surroundings, good for commuting or working in coffee shops.
Although I find the sound a bit more dull and less fun than the PortaPro, whatever I think these may lack in sound quality, they make up for in features design and comfort, making them my go-to portable headphone for the time being.