Everything I could've asked for here. I wanted to be able to use this both with my phone (for calls and music) and, as I live in a small flat, I thought it'd be ideal for keeping the noise down when using my PC for music, films, gaming etc.
First thing I noticed was the packaging; compact and easy to open, no evil clamshell plastic, easy to repackage again if you want to return it. Not a big deal, but it's a nice change. After that, pairing it with my phone and PC was completely painless, and the volume and back/forward buttons worked with both out of the box (not sure why another reviewer had trouble identifying them - if you wear the band behind your neck as intended, they're always in the same place...)
The things that mattered most to me about this product though were Portability, Comfort and Audio Quality.
PORTABILITY: It's wireless, obviously. It also collapses down pretty well as you can see, and it comes with a draw-string dust bag, which helps keep it alive in your bag or pocket. The recharge time (via USB mini cable, included) is pretty short, and the battery life way outstrips my phone, so no problems there. The range quoted is also pretty conservative - no problems within the same room as the transmitter, and mostly even within the same house.
COMFORT: In spite of being collapsible, and very light, it's also pretty sturdy - I put this down to the fact that it's not adjustable. Hasn't been a problem for me, as it's far more comfortable in extended use than in-ear phones or big cans. The lack of a cable means you can have your phone in your pocket and not worry about tugging at it (plus you don't have to hear the cable rustling in your ear every time you move.)
AUDIO: Bluetooth isn't designed for perfect audio fidelity. However, if you're not a serious audiophile then you'll be very happy with the reproduction from these. Well-rounded, good range, decent bass - not bad for wireless headphones under £30! The big multifunction button (call/pause-play) is surprisingly loose and rattles if you bobble your head about, but it hasn't bothered me yet. Still, it's the one black mark. The microphone is much like other hands-free types - it's fine, but I wouldn't recommend it for noisy environments or outdoor use.
One warning: I thought I was having trouble with the headset dropping out of stereo into l-mono depending on the audio frequency. The seller happily offered me a replacement, but some googling revealed this is actually a known problem with the bluetooth audio stack in the Samsung Galaxy S2 - it was my phone's fault all along, I'm afraid. The headset's been fine with other devices.
Overall, I'm extremely happy with this kit, especially at this price.