You're not buying an inflationary currency. The inflationary currency is what you buy things with. Like commodities (bitcoin)!

Bitcoin (or any other commodity/crypto) being valued well and being a "good" investment is completely detached from its function as a national currency. One does not (and should not) imply the other.

You need something to exchange things with (currency), and you need things to exchange. The currency is the medium of exchange, the journey, not the destination.