Although I don't doubt your friend's sincerity, as a Christian I cannot agree with this group's teaching. Let me explain why.
The issue your friend raises isn't simply a dispute over a minor point of belief (as sometimes happens among Christians). Instead, it involves the very foundation of our faith. The reason is because it deals with a very important question: Who was Jesus Christ? Your friend's group apparently answers this question by saying that Jesus might have been a good man–but He wasn't the Son of God who can save us from our sins.
The Bible tells us otherwise. It tells us first of all that Jesus was God in human flesh–and because of that, we don't need to look for a later prophet. He is God's final message! The Bible puts it this way: "In the past God spoke ... at many times and in various ways, but in these last days he has spoken to us by his Son" (Hebrews 1:1-2).
The Bible also tells us, however, that Jesus Christ was God's final sacrifice for our sins. Our greatest need is to have our sins forgiven–and Jesus made this possible by His death and resurrection for us. Give your life to Him today, for "Salvation is found in no one else, for there is no other name under heaven given to men by which we must be saved" (Acts 4:12).