Burislaf was also a markgrave of the Saxon empire. The Royal and noble genealogy of UK lists Mieszko I as aka Burislaf von Wendland of Wendland (Wendish land in northern Germany). Mieszko I , recorded Miecislaw (or something like that) may have been a name much later given to him by Polish writers, since the only record seems to be as Dago in Dagome Iudex. Since Ote is mentioned in this, I believe that this is the record for Mieszko I and wife Oda (von Haldensleben),when by marriage to her he (Dago-bert ?) accepted the position as margrave of the empire.
To the christianisation, all dukes, margraves etc had to axcept baptism as part of receiving the position from the emperor ( see Moravians (Czechs, Slovacs) who came before the emperor in Regensburg before 900 AD). German kings/emperors never made any demarcation line between Slavic and German people or any others, such as Huns, Finns, Esthonians etc.
Taking on the required state religion and name is typical of the Russian rulers or any others also, where Sophie von Anhalt-Zerbst , took office as Czarina Catherine II and became orthodox. When Russia conquered the North the language of Couronia, Livonia,later Latvia continued to be German until 1891.
When you look for records, write down the current writers of the article, but also check for primary sources. This is what JHK keeps asking for. The primary source is ,when and who first recorded it.
I have read something to the effect, that the Dagome iudex is a 'gift certificate' , with which Dago (Mieszko I ?) gave all the land he had conquered into papal possession. He then received land back in lien. This was a standard procedure, because all land of Europe was considered as belonging to emperor and or pope, who then granted liens (loans).