If you want to hide your transactions from friends and you're willing to go through a centralized company anyway, it's cheaper to use an regular exchange.
You can but there is a huge difference, centralized exchanges are custodial and KYCed whereby coinjoins are not, besides most coinjoin services are somewhat centralized anyway given that they use a centralized coordinator, which is why joinmarket is a superior option since they use orderbook over internet relay chat without a centralized coordinator.
Still, however, the worst coinjoin is probably better than the best centralized exchange when privacy is at stake.