So this leads to another question, is it a better/modern single stage regulator that will not EOTD and he just adds that in as a bonus to help sell the better needle valve, or are they still susceptible to EOTD since they are single stage?
It is call “output pressure rise", all single stage regulator have output pressure rise when the input pressure drop.
Good quality single stage regulators have less OPR than the low quality, for example, the Victor and Airproducts SSR have less than 0.1 psi rise for every 100 psi input pressure drop, so excess co2 injection when the co2 near end is really a small digit.
low quality SSR sometimes have OPR more than 0.5psi per 100 psi input pressure drop, it is troublesome because if initial output pressure is low, the total OPR is a fairly big fraction, means more excess co2 injection.
for example, if you set the output pressure at 20 psi, on low quality SSR, the total OPR is 4 psi(0.5*8), makes the actual output pressure at 24 psi, about 20% pressure increase. The actual excess co2 injection volume calculation is complicated, but you will have good idea excess co2 volume is proportional to that the total OPR, higher the OPR, more excess co2 injection.
there are ways to avoid large amount of excess co2 injection, first, a good quality SSR with low OPR. Second, up the initial output pressure, the total OPR is a small percentage compare to the initial output pressure.