a note from David VK2DRT
A new developer has added greatly to the firmware of the GPSDO and has a vastly improved readme at the link below to help both programming and developing.
Suggestions and development continues are more people come on board.
Others have engineered little daughter boards that fix the output impedance/amplitude issues should that be important to you. It may not be perfect but it greatly exceeds the accuracy of my old frequency counter which is now bang on (once given an hour to warm up lol).