Yes, I should've made it clear that for effective maintenance you need fabric component strop, not just leather. There are some old threads with experiments on the difference the fabric component makes.

I have tons of strops but have been using essentially one of them (plus a vintage kanayama shell for 10-20 laps at the end). The fabric component on it is cotton, that is treated with something waxy - that's the most common vintage strop as far as I can tell. This one started brand spanking new looking and over the first month started graying and now few years later is fairly black. That's the iron oxide from the razors I've stropped and it seems a good thing on a strop. I am not sure what is currently the dominant abrasive, the iron oxide or whatever treatment the strop started with, but if I'm to bet I'd say they're likely comparable.
I've also used plain vintage cotton, linen and few different treatments and they all work.