I brought one off ebay its ok, you cant really feel anything when your inhaling. Its like inhaling steam, you can feel a slight nicotine hit. I used one when i quit smoking.
Unfortunately mine broke after a few weeks :-/. Might of been just a one off, but have a look at the ones with a blue LED tip they are meant to be better quality.
You charge it up and then you buy end tips, you can buy them in different strenghts and flaovours one tip is equivalent to about 20 cigs.