Not a scam. It helps kids have braces for shorter periods (though yes, it may be split into two periods--it's just silly for the dad referred to in one post to say "I'm not paying for it twice" because he will probably end up paying the same total if he insists on waiting and doing it only once--later, when the palate is harder and the teeth more set).
Expanding the palate while it is still soft enough to move is very wise. If you wait until it has hardened, it is MUCH more difficult and painful to do the whole deal with braces etc. I had braces in junior high/high school and I know that if I'd had them the way my daughter is doing it, in probably two sets with the first ones including a palate expander, my life would have been much easier and my time in braces a whole lot less.