If memory serves, the word "advertisement" in French means "warning." Judging by an ad I saw on this page just now, I would echo to this, "Amen."
The ad in question says Mormons believe Jesus is the Savior of the world. True. Their theology does teach this.
However, one cannot say they are Christians. Why? Because Christians -- in order to be such -- must be Trinitarian. That is, they must believe in one God in three Persons: Father, Son, and Holy Spirit.
Mormons will profess belief in each of these, but they do not believe they are all One. Jesus is the Son of God the Father, but He is not, in the words of the Nicene Creed, "consubstantial" (i.e., one) with Him. Also, and in the same respect, they neither believe what the Eastern Orthodox or the Latin Church believe about the Holy Spirit.
Ergo, they are not Christians. Buyer beware. Our Lord spoke about false prophets. This is just another example of what He meant. The Mormons are basically modern day Gnostics and Arians.