I have had it done and the only one who noticed was me. It did take away a little stain I had, but I wouldn't bother again. I would be cautious if you already have sensitive teeth, I remember it was quite uncomfortable for a few days. 250 doesn't sound that cheap either.
I've had mine whitened and I'm having it done again this week. It does vary a lot depending where you have it done and what sort of whitening you choose with your dentist, plus you then have to keep it up at home for good results. I think it's worth it personally x
I was chatting to an elderly man recently who had obviously had his teeth whitened. They were as bright as snow. He was American. His teeth looked good, but very fake. It was startling really.
I'm thinking of having my teeth whitened, but not to that extent. Maybe just less yellow ;/
I also have sensitive teeth so wouldn't consider it. A friend spent a lot of money having hers done and you wouldn't even notice any difference. IMO if you have reasonably good teeth I would leave well enough alone.