"If it is possible to imagine one private electronic currency, then its possible to imagine several, and there would be no guarantee that other people would accept the particular electronic money you use."
IMO this is an interesting issue that hasn't been addressed enough on this forum.
To me, there is no guarantee that other people would accept any currency anyway, unless they are forced to. Money should not get its value from coercion, but social acceptance. Moreover, even in a word with many competing cryptocurrencies, commercial transactions with anyone are possible, as long as there is an efficient currency exchange market.