Nothing tbh, they're all the same just material wise (mesh, circa knit, swede, prime knit) . Theres also the City Socks (prime knit) and Chukkas (Swede) NMD.
My feet is weird if an 8.5 NMD has half an inch of toe play and quarter inch of toe play for 9.5 UB. I need some room tho so I'm good. It's up to that guy ^^^