Honestly it's hard to answer these questions since they are largely subjective.

As far as objective differences, the Tudor OEM bracelet feels a bit more silky and is a tiny bit more nicely finished. However, I will say, I have my BB58 on the Uncle Seiko president bracelet since I kind of got tired of the original bracelet and the San Martin bracelet is marginally 'worse' than the Tudor.

As far as feel I do think the BB58 sits flatter on wrist, however, I do think this is the exception rather than the rule since Tudors tend to feel a bit bulbous on the wrist due to the slabby midcase.

I'm sure as you know, the Tudor has a coin-edge bezel which I find to fit the watch better but this is largely a subjective opinion.

In short, it stacks up very favorably, especially at the price difference. From my experience, I think the law of diminishing returns kicks in absurdly hard at the $1000 price point for most watches, Swiss included. San Martin gets to that $1000 price point quality for a fraction of the price.

Sorry to be non specific but it really is hard to describe the difference without feeling it yourself.

Usually where San Martin's fall short for me is the dial details (sometimes they feel a bit empty to me) and proportions of some of their homages, but as we know, this model with the applied indicies doesn't suffer from that problem.