Beeing in school myself, i know that these sites are not the best of choice to use.
Copping essays from them will result in all of your examinations canceled, as has happened to 2 of my friends.
I myself wouldent buy one from a site like that. I would first try to write it myself, and even then if i get stuck, i could always ask a friend who knows everything to give a helping hand. This is also free, believe it or not! LOL!