Well I have also built a GPS disciplined oscillator using an Arduino and the Adafruit Si5351..
It works well and the frequency is very stable.. I have compared it with a Commercial 10.000,000 mhz time base oscillator and it is spot on..
Hans prog rock should work the same.
I do have a spare prog rock sitting here so I am going to give it a try and see how it does.
The prog rocks I have in service I find are very good and do not drift ( using the TCXO's ). The TCXO is the key to stability at least that is how I see it.....