Prizechecker.com is legit but you're most likely not going to get anything out of it, aside from lots of pressure to buy a car. The goal is to get you into the dealership so they can sell you a car. The most challenging part of selling a car is getting people to come in, so dealerships use things like this to entice people to come in. If you come in with one of these, you look like an easy sale for falling for this.