A coated reservoir presents no operational problems, save the pin point bleed hole nearest the brake line outlet.
That tiny hole must be cleared, yet remain tiny. A narrow pin or needle can be used to clear it if you are careful. I've also used the tiniest drill bit in the Xacto tiny drill bit set; #80.
However, there may also be a hard coating in the master's piston bore. I remove this with aluminum oxide paper placed in the end of a wooden dowel that has had a slit cut in one end. Then spin that in the bore with a drill.
Ensure that the bare piston without rubber bits can move freely in the bore, and you should be good to go for assembly and use.
Cheers,