As I was commenting on my experience with the Berbers in another previous post, a little before the confinement in my country (Spain), I managed to complete what has been the greatest challenge in the SAI. A total campaign, with the berbers.
It took me two centuries to complete the domination, since the only rival of the berbers (Eranshahr) controlled all of Asia, with select troops that at any moment could face mine, in addition to pointing out that the native berber troops were grazing sassanid cavalry. That is why I had to reorganize my armies based on roman units, the support of (vital) mercenaries and the constant use of war machines, fortifications to protect myself from any sassanid attack (impossible to fight in pitched battle, except in the case of use mercenary veterans, such as an army entirely of sarmatians and alans who saved me on more than one occasion).
As a colleague warned and I myself assumed, campaigning with the berbers is SUICIDE. I finished it for honor and with a lot of headaches. It was a joy to take my berbers across the Indus and complete the destruction of Eranshahr, using their own iranian and armenians troops and mercenaries of all ethnicities.
P.D.: it was a real nightmare to send my troops to kill some sassanid units. On more than one occasion, a pushtigan unit killed 4 or 5 mercenary units (even though they already had a lot of experience) besides several units of bodyguards. I have never felt so powerless with a faction.