KVS scrapes data from otherwise-available sources, though in a very useful way IMHO. ExpertFlyer pulls data from a CRS. Each has strengths and weaknesses which vary based on what airline you use and what you're trying to accomplish. I do like that ExpertFlyer has an email functionality, it'll continue monitoring your desired availability and email you when it turns up.

If you fly AA, you want ExpertFlyer. I love the ease of searching *A awards on KVS (though I could do it myself on the NH website).