My response would be that, taking two readings with one pull does not ascertain that the proper amount of tension has been placed on the tape. Two separate measurement actions would go further to assure that the proper tension was applied. Similarly, if, by chance, the beginning end of the tape (opposite the end being read) happened to slip a quarter-inch (or 1 cm) due to pavement giving-way, you wouldn't have a second measurement to cross-check against.
Simply reading two indicators with one pull only verifies one aspect of the measurement. If we put two counters on a bike, and read them both at each split (and overall length), we would only verify counts for the path ridden; it does not verify that the ridden path was the SPR. I think pulling once and reading two different scales (metric and SAE) is not a good indicator that all the variables have been double-checked.