When I think about problems with Customary Units, I think not about decimality, but that the units are too disconnected. For example, there are BTUs and HPs that mean the same thing (power), but are wildly non-connected both to each other and to other units. While in SI, a Watt is Joule per second, a Joule is Newton times meter, a Newton is kilogram times meters per second squared, and voila, you have arrived at basic units. Your AC, your PC and your electric car have power consumption in the same units, and the same units are on your bill. This is what valuable, and not Greek prefixes.