I have two 7". They are bright. I paid 79 each on sale thanks to a hint from Potatomutato! Those little 4" from wallymart are crazy bright for the little package and low cost. the two sets together are more light than I need. Working on a set of small fogs now.
They draw more power so depending on what you have now, may need to be replaced. I think they come with 12 or 14 ga wire with in line fuses, pretty nice package they are.
I've heard pretty good things about those HIDs. I would have gotten them myself if they weren't so expensive (especially for coming individually). I went with Kragen's KC Daylighters instead since they're the same price, but come in pairs. They're decently bright too. Comes with in-line fuses and a nice switch with an LED light.
I think I need to get a bigger alternator because when I have all 6 KC's on, it bogs down my engine.