Pulpdent's Embrace brand sealant is, and always has been, BPA free. Great product that I've used in my office now for about 5 and a half years. And no, they didn't change the forumla after the BPA story last winter, just their marketing campaign a bit 😉
As for the sealant vs. composite comparison. Basically think of a sealant as a composite resin that is has a lesser amount of filler particles in it. Are there some other, minor differences, sure. But basically a sealant is just a "lesser" filled resin restorative material than a composite