Performance, as I said earlier, is very good and arguably the WP-350's strongest point. In going wireless with Bluetooth headphones, you usually have to give up some sound quality because Bluetooth compresses your music and has a tendency to flatten out fidelity. You'll experience some of that with these headphones, but the sound quality holds up well against that of comparably priced wired headphones.
The WP-350s offer decent clarity and deliver a good amount of bass. They also play loud and work pretty well with all types of music. These are by no means audiophile-grade headphones, but I thought they sounded better than a lot of in-ear Bluetooth headphones I've tested, and delivered almost as good sound quality as the pricier AKG K830BTs (also an on-ear model), which cost significantly more and aren't as comfortable to wear. I also thought they were superior to a pair of JayBird Wireless SB2TR Sportsband Bluetooth headphones I had in-house.
As far as using the WP-350 as a headset for making calls, it's only fair. You can hear callers quite well but because the microphone is housed in the right earcup, it's a little far from your mouth. My test callers said my voice sounded a little muddy and slightly muffled. They could hear me, but I just didn't come across totally clearly.
Finally, battery life is rated at 8 hours on a single charge, which is a standard spec for Bluetooth headsets. I was able to use them for a full week on my daily commute without having to recharge, and I travel a little less than 2 hours a day.
Creative's WP-350 Bluetooth headphones won't blow you away with their design or comfort level, but their performance in those departments is capable enough to justify the affordable $70 price.