from Moto Site this is only for a limited time on on the Moto Z line (all other phones show similar markup on Affirm financing)
Motorola has the right to subsidize it’s phones it sells directly to the end customer,
note the Moto Z , Moto Z Play unlock phones are all GSM only (and right not even the Moto E4 and E4 Plus, and Moto Z2 Play are only able to be activated on GSM even though they have CDMA radios, and the Moto Z2 Force is not an approved Republic phone)
BYOD are GSM also so there should be no difference if you buy from Republic or Motorola.
due Not Republic’s GSM partner may not be a good fit for some 4G LTE + WiFi for the Best Cell Phone Coverage | Republic Wireless
(also note T-Mobile is republic partner)
edit to update the Moto Z2 Play information