I guess one of it is bitrefill. They're not just tools but actual services that do offer other services and products in payment of bitcoin and other crypto that they support.
As you've said, it's a digital currency so it has to be spent. Whether you're spending it on trading, that's fine or the same as bitrefill then that's okay as well. That's the sole purpose of it as an alternative payment to the traditional payment methods we've got.
I have never used crypto currency to spend anything at this point so when I want to buy any goods or services, I always exchange my digital currency into fiat currency so I can do traditional transactions as usual.
So if bitrefill can serve things differently at this point, I'll try to explore it when I have some spare time.