Why use an eSIM in Tanzania?
A Tanzania trip is usually two trips joined together, and both are awkward for connectivity. First the safari circuit out of Arusha through the Serengeti and Ngorongoro, or a Kilimanjaro climb from Moshi, where you are in a vehicle or on a mountain for days. Then Zanzibar, where the pace drops and the phone comes back out for boat trips and dinner bookings.
Local SIM cards here are registered biometrically, which for a visitor means an operator shop, a passport and fingerprints before the line will work at all. That is not what you want on the morning your safari vehicle is leaving. Landing at Kilimanjaro (JRO), Julius Nyerere in Dar es Salaam (DAR) or Abeid Amani Karume in Zanzibar (ZNZ) with an eSIM already installed means you are connected for the drive to the lodge without any of it.

