At $400 (£349 UK, AU$549), the PM-3 is the least expensive model in the line and one of the least expensive headphones that use planar magnetic drivers, which tend to sound very coherent and spacious, with low distortion. What makes the headphone special is that -- in a world where most planar magnetic headphones have open-back (on-ear) designs -- the PM-3 has a closed-back (over-the-ear) design and it's one of the few planar magnetic models that's optimized for mobile use.
Open-back models generally offer more open, airy sound, but they also leak sound, which makes them less than ideal for use in the presence of other people.
The PM-3 is a good looking headphone. It's sturdily built, has an all-metal headband and hinges, and comes in white or black. It's also a comfortable headphone, though it's a tad heavy at 320 grams and does fit a little snugly (it offers good noise isolation). So I wouldn't describe it as ultracomfortable.
It's much easier to drive than your typical planar magnetic headphone and will work just fine with your mobile phone, playing with ample volume (it has a sensitivity of 102 dB). The new($700) also works with smartphones -- and so does the ($500) -- but the majority of planar magnetic headphones can't play all that loud plugged into puny, battery-powered devices (as opposed to home stereos).
The headphone comes with a 3-meter cable that terminates in a 3.5mm plug, a nice protective carrying case finished in denim, and a screw-on 6.35mm adapter for home stereos. If you order the headphones through Oppo's website, you can select a bonus cable (for free) that has an integrated remote and microphone. One cable is designed for use with Android devices while a second version is geared to ones that use Apple iOS.