The easiest way to tell if this is a religion is to do the "hotel nightstand" test. Ask them to see their texts and hear their cathecism, beginning to end. You already know the Christians go out of their way to tell you EVERYTHING about their religion, look in any hotel nightstand for the essential text. Likewise, ask any member of a major religion what their beliefs are and you will be told, for free, sometimes for hours on end.
Now, go ask a Scientologist for thier beliefs. You'll be told that you must be "prepared" to hear all their secrets. And, of course, that preparation will cost you tens or even hundreds of thousands of dollars. Just to hear what they belive in.
Actually, since most cults don't cost anything to join, you are probably doing them a disservice to call Scientology one.