First things first: well built, easy to fit unit. I fitted it to a 2000 Vectra, including an adaptor to make it work with the steering wheel remote controls, and hooked it up to the sub & amp at the back. I installed the microphone up at the top of the A-pillar, with the cable behind the trim and running down behind & through the dash - easily done, and plenty of spare wire.
The audio sounds good - far clearer than the cheapo Tevion unit this replaces, and better than the stock Vauxhall (Delco) unit too.
Bluetooth hands free is pretty easy to set up and a delight to use - dead easy to answer an incoming call (just push the big volume button), and start talking - caller is loud and clear (with volume adjustable via the volume knob of course), and people I've spoken to said I was loud & clear, even when driving along. Making calls via the unit rather than the phone is easy too, with quick access to recent calls / missed calls lists etc, and easy phonebook searching.
Unfortunately the phonebook originally displayed in Last name, First name order, and I found no way to change this, which annoyed me somewhat. However, I since installed CyanogenMod 7 on my phone (a HTC Desire), and the names are now in the First Name, Last Name order I wanted, so it appears the order in which they appear is down to the phone, not this unit.
Radio and CD playback and aux-in are fine (not a lot to say here, it just works as you'd expect).
MP3 playback is good, but unfortunately the tracks seem to play back in the order they're in on the filesystem, not sorted by filename or ID3 track tag, which is a real pain. If you have e.g. 01 - Song A.mp3, 02 - Song B.mp3, 03 - Song C.mp3, with appropriate track number ID3 tags too, there's no guarantee that they'll play in that order, which ruins mixed albums (and ebooks, if you're in to that kind of thing). I've not found a way to get the unit to do sensible sorting, so you'll need to use something like the "fatsort" utility to make sure the entries appear in the FAT filesystem in the correct order. That's not something I think the user should be left to take care of on a decent, reasonably expensive unit.
I haven't used the unit with an iPod/iPhone (I'm not an Apple user), but I've used it with a USB thumb drive connected to the USB port, and it works well, other than the aforementioned issue of track playback order.
If you're using a USB thumb drive, be aware that it will stick out from the front of the unit a fair amount; depending on the vehicle, it might be likely to be caught and damaged. I'd recommend picking up a short USB cable with a 90 degree plug from eBay for a couple of quid - plug that into the slot on the headunit (the 90 degree plug won't stick out much), then plug the thumb drive into the socket at the other end of the cable.