I've been very happy with the original PX100. When I saw Sennheiser had improved it, I was reluctant to get the new model after I lost my current set on a trip to Barcelona. But then I found this model with the iPhone controls.
Unlike the old PX100, this model doesn't come with a hard travel case. In fact, the collapsing arms are a bit wider now so the PX100-IIi no longer fits in that case. I comes with a little pouch, though. The arms still fold in and the earpieces rotate 90 degrees, so the pouch is good enough if you carry the headset in a pocket or a bag, but I'd still be careful.
The sound is good as ever, with a clear high end that lacks the harshness that I've often encountered in cheap headsets or earbuds. The bass response is notably stronger than with most other headsets, but in a good way. It's really a pleasure to listen to music with the PX100-IIi. You can turn up the volume as high as it needs to go without distortion or resonances. From memory, it seems I need to turn up the volume a little more than with the old model to get the same level of output.
The old PX100 had a cable that split and went to each ear individually. With this one, the cable goes to the left ear, which turns out to be more pleasant. There is a little clicker in the cable which allows you to control recent iPhones, iPods and even Mac computers. The volume up and down buttons work very well, and the play/pause area is ok for stopping and starting playback, but double or tripple clicking isn't as easy as it could be because there's no separate button, you have to squeeze the middle of the clicker fairly tightly. There's also a microphone in there, allowing you to take calls, record voice memos or issue voice commands.
The headset is light and doesn't squeeze the ears much, so it's easy to wear for long periods. It's a great general purpose headset, but not ideal for exercise (sweaty ears and foam earpads don't go together well) and there is zero isolation from outside noise.