Hello Alex,
I have no information at all on the MA4258 secure microphone. I can see that the programmer for use with it is the MA4255/MA4254. I understand that the MA4255 is the Master Key Fill and the MA4254 is the Slave Key Fill. The MA4255 can be used to fill the MA4258 directly, or fill via the slave unit, MA4254.I can't say that I have ever seen nor used any of these units.
I hope that this helps!
73,
Peter
