Hello Bernard,
from a quick look at the code, the "save all" function is not implemented in the current master, and there is developer's comment explaining that who ever wrote it was not sure how the "save all" should work. However the save function for single channel is implemented and that can be reused in save all, which makes the needed change pretty trivial. An idea that comes to my mind about how the "save all" could operate - you enter a single "file name" and than each channel is saved to file called "file name" + "_channel number".
I'd normally quote this at 2h and $100, but i've tried compiling the code with my current setup and there seem to be a few issues that need to be addressed to get the code to compile with current versions of everything and that would probably take another few hours to finish.
As for the balance board for testing - i do not think that there is a real need for one on this side, this is a very straight forward job, and i think it would be sufficient that you verify the functionality on your side. Worst case scenario - we could remote and test it together on your setup.
Also the delivery time i've listed is just to be on a safe side, because i'm not sure how much time the setting up of the project to compile will take, but is likely to not take longer than 1-2 days.
Kind regards,
Emir C.