Except he is using GPS as a very precise 10MHz signal, not a clock. The private rubidium clock (about 1500USD from memory) will provide that very nicely.
Personally if I was running an experiment that required that sort of precision then the private highly accurate frequency source is going to be fairly small beer in the total cost of the experiment and freezes you from the trouble of getting the GPS signal into your lab, which for most labs I know is going to be a right pain in the backside because GPS signals don't extend indoors. Further more is there is not chance that some random event won't knock it out for a few seconds and potentially ruin your experiment.
I guess the point is that until recently using GPS was a valid way to get a very high precision reference frequency, though here in the UK I would suggest that using the BBC Radio 4 LW signal might have been a better idea. The carrier frequency is controlled by a rubidium atomic frequency standard for the express purpose of enabling it to be used as an used as an off-air frequency standard. However time and tide move on and now it is not such a valid choice as it was previously.