This is basically using fiat for purchasing stuff, and you just automate the selling of your BTC to a centralized platform that already has your Bitcoin.
Not your keys, not your coins.
A better way to use your sats is to use lightning with a card, like Bolt Card, or a similar one. You can pay with your card in-store by tapping, and it connects directly to your own wallet, and uses your sats from your storage. No third party needed, no dirty fiat conversion.