their prices are fantastic, especially if you book far enough in advance. I flew London to AMS for 25 bucks! Most of the price advantage disappears as the date of travel gets near. The comparison to SW is appropriate. You may need to bring your own snacks/beverges - I don't remember.

Also, sometimes they use suburban airports. You have to do some homework to figure out how to get to those airports. For example, a cab ride to London Luton airport will devour your savings, but there is a resonably priced train from Victoria. Their website has a lot of useful info.