As regards JMP that is Jerry Walker (I think he is a member on this board) and I can vouch for the reliability and quality of the products I am sure his PROMS will be tested. You only have to watch his dedication to restoration on the youtube channel to see that - watch the latest series on the MADAS calculator and how he has to fix the motor-
https://www.youtube.com/watch?v=HkWtbaMCPnM
Do watch out though anyone using the MK14 board as it has a different KB connector layout if using the PI/Arduino programmers elsewhere, they need a tweak in software and some extra opto isolators if you want to use them on both boards interchangeably.