I've never seen a Marmont bag in the wild unless I'm carrying it

I have an Antigona too (which I plan to let go of) and I've certainly seen a few of them being carried. I'm letting go of the Antigona though because although it's classic and lovely to look at it's a structured and bulky bag, which I personally don't like to wear. I can vouch for the Marmont leather being hard wearing and the metal chain and logo is still looking good after two years of wear.
As others have already said, the style is a classic shoulder flap and given it has a much better price point than Chanel, IMO it will probably stay popular for a while.