If you don't live in the Netherlands using iDEAL isn't really an option for you. Given how quick, secure and efficient it is, that is a bit of a downside.
If you're a Dutch user there really isn't anything to steer you away from iDEAL as a payment method. You do access your bank account to make the transaction but your details are highly protected and secure so there's nothing to worry about.
As always there can be email phishing attempts with phony iDEAL logos to try and gain your log in details but as long as you only deal directly with the cashier page in the online poker client you're never at any risk.