Have to agree with James and Mech.
The TDI course instructor required that I had required that the students check several tanks of nitrox of an "unknown" oxygen percentage in one of the final segments of the class, which, of course, gave the students in verifying gas mixtures.
I don't know how diving a tank or two of nitrox can create a more capable nitrox diver than not diving them, other than the fact the the other diver now has two more dives.
OK, don't start a war but IF a diver were to make two dives on an unknown gas mixture, what added experience or knowledge has he gained.
Please don't start with the, "Well, he should never dive an unknown gas" position.
By the way, does everyone analyze a tank of air before they dive it to make sure it's EAN21?
But, as was stated above, if the cost of the class includes the cost of the two dives and is equal to or less than the class that doesn't require the dives plus two dives, then it's a wash. Do the class that includes the dives.