Is it? Damn! And here's me using it as a currency to buy a huge variety of goods and services for years, both in person and online, from around the world.
NO ONE is pricing their products in Bitcoin and using it as a currency. When you pay by Bitcoin, it is instantly converted into US DOLLARS that the seller uses. You can NOT price things in Bitcoin, it is to unstable.
1. If you were hired at a job last year, and paid in Bitcoin, and your pay was actually priced in Bitcoin, at a rate of 1 Bitcoin per year, would you still be working

2. If you put your house for sale on the Market in Bitcoin last year, actually priced in Bitcoin, 10 Bitcoins for your house. Would you sell it today for 10 Bitcoins

Using Bitcoin as a currency IS A LIE if it is nothing is priced in Bitcoin, the bitcoin is instantly converted to US Dollars, or whatever the currency your country uses.
SORRY, converting your BitCoin to US Dollars to pay for your tesla is NOT bitcoin functioning as a currency. Even if Tesla does the Bitcoin - US Dollar conversion for you, the PRICE is always a US Dollar amount.