As I posted before the SD is an excellent quality buy for what it costs. Imo the only mod to evaluate is changing the crown (unless You have mismatched lume on the hands and markers). If the intention is to do all the mods (TC dial and hands/ TC bracelet/crystal etc.) and You have to send it off to a modder to do it, it´s not worth buying and to go right away for a TC sub is the better choice. TC as a submariner is thinner, the BP SD has exactly the same thickness as the gen SD. Imo it´s also not worth buying the TC bracelet as the SD one is very good already. It´s for perfectionists who want to have it 0,01% better only. It´s under a 10x lupe that the TC dial reveals all it´s unmatched smoothness and class. As long as they are not side by side differences are minor.
With me and long-term TC, SD and BP Sub-C get the same wrist-time depending on the mood and where I´m going. Unmodded SD versus TC Rouge