Indexing offers many advantages for investing, but not all index funds are created equal. For the leading index products, low cost is a big attraction. But in a world where indexing choices have exploded, caveat emptor applies. “Most investors assume, however, that indexing automatically means getting a cheap fund and certainly one that’s cheaper than an actively managed fund, Morningstar’s John Coumarianos advises. “However, this isn’t necessarily the case.”