In my seminary work, I did a survey of Montanism. There are a number of histories that detail their heresies.
The Donatists were much more normal, but believed that a pure clergy was necessary for the ordinance of baptism. I am not sure I would consider them heretics in the same vein as Manicheans or Arians.
That being said...
As a believer in the local church, I do not need to follow either the Catholic Church or the schismatics. I believe that scriptural local churches existed in either or both sides of these schisms. I can not deny that and still be a believer in the scriptures.
Jesus' words in Matthew 28 were very clear to me, "Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you always, even unto the end of the world. Amen."
I am with you until the end of the world. The injuction was clear... go, evangelize, baptist, and catechize until the end of the world. Jesus will be with you as you do. If there was no scriptural baptism for hundreds of years, the Jesus was a liar to promise it.
Further, there is a scriptural pattern to the way that someone is scripturally added to the church. According to the description of Luke in the book of Acts, "those who accepted his message were baptized, and about three thousand were added to their number that day" (Acts 2:41).
The biblical pattern is salvation, then baptism, then addition to the church. This pattern must be followed in order to have a scirptural assembly. The Lord in his Word several times promised that such scriptural assemblies would perpetuate throughout human history.
I believe Jesus!
Which is why there are histories that detail the history of those, who, according to the Martyrs Mirror were "baptized only upon Confession of Faith...." Yes, there has been scriptural baptism throughout the ages. Those congregations who baptized those who had already come to faith. Baptists are part of that movement that started with Christ building his first church during his personal minsitry.