These last a looooooooong time!
I bought these to put in centerpieces for our wedding, and we had tons left over. They lasted through the entire ceremony and reception, 10am-7pm. We saved the extras and used them two weeks ago for a cocktail party (they were randomly scattered around the house, in vases, candy dishes, etc.) and left them on all day, night, and week. 9 days later, they're still lit (albeit faded). These little buggers had quite the life in them.
If, for some reason, you can't use real tea candles, these are well worth your money.
ConsLots of plastic to throw away. Unless you're seriously restricted from using real candles, just buy tea lights.