The point is that their system is not really more useful than the alternatives. But once you convinced a country through your PR, they'll be locked in and the cost of switching to something marginally better (and less costly) may not be worth it. So no, just that they have customers is not proof that it's the best option.

Also, "if it's not useful, it won't have customers for long" is quite obviously wrong. See e.g. essential oils, homeopathy and so on.