they're a dutch airline; if you're coming from the uk you'll have to fly to amsterdam, which could be as expensive as the martinair usa flight, particularly on a klm route with no competition. it will add an hour or 2 to your journey, but does allow you to fly from your local airport.
martinair are cheap, but you get what you pay for. personally I wouldn't fly to the usa without upgrading to comfort class because economy is too cramped for me.