Thank you for your long and detailed answer and sharing your great knowledge. Well, I am badly surprised about the KWS attitude towards animals donations, in particular concerning rhinos, as multi-national cooperation is one of the keys to ensure the protection of the species at a continental scale, through creation of new population while boosting birth rates.
I had no idea about the reintroduction sources for Mkomazi and Singita-Grumeti. Rhinos would certainly be better protected in Singita-Grumeti than in Serengeti, though I guess it is legitimate some of them go to the Serengeti. An as far as I know there is no fence between both protected areas so rhinos would be free to move to the better habitat in there.
APN is currently working in reintroducing rhinos in Zakouma and Akagera.
While I understand it is legitimate reintroducing black rhinos in Zakouma, even if they are not from the same sub-species (western black rhinos went extinct a decade ago), black rhinos were actually introduced in Rwanda according to APN. If it is clear multiplying rhinos population is good for ensuring their preservation, it is clear in this case APN tries to use the Big 5 as a comercial asset in promoting Akagera and get larger incomes. I would be interested to get the opinions of different persons on this question.
On the other hand, it is important to maintain some captive eastern black rhinos for breeding programs. Who knows what the human madness is really capable of?