I keep Polkadot coins on Binance Exchange.
To participate in airdrop, testnet or IDO events I usually send from Binance Exchange for Polkadot coins.
If you think it's expensive for a hardware wallet, then the method above is an alternative for us to store Polkadot coins.
Binance exchange is popular exchange this is a reliable platform , but holding your investments in exchanges for long term it not a good decision because it is too risky instead of we can use best online wallets they're free to use also they're providing many futures safepal is a best online wallet to store Dot.