The 'Soft-nose Split' was basically one of the three standard options for Nitro-Express cartridges in the hey-day (the other two were soft-nose and solid). Much like today choosing between a FMJ, soft-point, and hollow-point. Yes, the splits were designed to promote rapid expansion. In a .470, they would be OK for lion, but in the ~.400 class of cartridge, which was looked upon as more of an 'all-rounder' in those days, the split bullets were for antelope and pot-shooting. This increased the versatility of a double nitro-express for the 'one-gun' hunter.

Soft-nose Split bullets are discussed pretty thoroughly in the texts of the day, most notably 'African Rifles and Cartridges' by John 'Pondoro' Taylor.