The company's first product launch failed to attract significant customer interest. Its second product, ______, sold out within days of…

The sentence sets up two products with sharply different outcomes, and by comparison is the natural way to frame the second product's success against the backdrop of the first's failure. In other words signals a restatement of the same idea in different words, but selling out and failing to attract interest are opposite outcomes, not restatements. Namely introduces a specific example of a category just mentioned, which doesn't fit here. Granted signals a concession before pivoting to a counterpoint, a different rhetorical move than a straightforward comparison between two products.