An excellent effort; proper execution of experiments is independent of the sensitivity. It's very inexpensive to get good at the science and art of experiment itself. Proper execution is the hardest part; improved sensitivity is in significant part a question of available resources (cleverness is significant, too).
(The precision-metrology part of me feels compelled to point out that any absolute measurement of the speed of light using this method should include an estimation of the covariance of the result (and its uncertainties) with the variation of the assumed value of c used by GPS for timing and position determination).
That, and the citizen science movement helps tremendously. It's what I love most about eBird[0]. Thousands of people collecting observations (with varying degrees of accuracy) provide a wider and more accurate picture than any number of scientists could deliver on their own.
(The precision-metrology part of me feels compelled to point out that any absolute measurement of the speed of light using this method should include an estimation of the covariance of the result (and its uncertainties) with the variation of the assumed value of c used by GPS for timing and position determination).