What am I missing about Goldbacks?

So besides the neat pictures on it why buy goldbacks? Doing the math the FL $100 GB is 1/10 troy Oz but is 5 plus some change per dollar. So like 540 per 1/10 ozt. Seems like I’m missing something, why not just buy a 1/10th coin? Hell damn near 2 1/10th coins for the money.