you have mistake about calling Bitcoin a currency. Bitcoin is Money, Bitcoin worth it's price as like as gold. but using it as currency with high fees, slow transactions, while there are better coins as like Litecoin, Bitcoin is no longer a currency these days.
I'm Bitcoin user since 2016. I'm holding and spending it to buy products before. but recently it's almost impossible to use Bitcoin as currency like it was before.
My mom tell me about old days, they was using Gold to buy cheap products. now they use Gold as Money, you can't go and buy from supermarket using gold easily as like our parents did before.
same happening now with bitcoin. it won't be usable as currency for cheap products.
It is still money depending on what you are buying, especially if there is an off-chain option. For example I do my namecheap expenses from bitcoin, never used my credit card, and I just put 100 bucks in there and spent about 4 dollars on the fee as well and it was there about 18 hours later (didn't matter, didn't want to put 10 bucks in it) and that was fine, I have spent the same thing for 8 months or so now and I will probably cover another year of expenses from that or maybe put in a little bit more (can use alts as well).
Same goes for places like expedia and booking where you can arrange your vacation, between flight and hotels? That's gonna cost you quite a bit, especially in a European vacation that would be above 1-2 thousand euro easily, spending another 10 bucks or even 20-30 bucks wouldn't really be that shocking, so I would say it would be fine. Long story short it is still a currency, just for bigger things.