Using a Check Card is fundamentally risky. A debit card secured with a Pin # is still secure; however, besides gas stations and supermarkets, very rarely are debit cards accepted. That is why the check card was invented - the problem is that it provides free access to your account.
If I go to a bar, for example, and hand the bartender my check card, because it is a Visa logo, it will be treated as a credit card. As with any bar, he'll authorize between $50 and $100 to be put "on hold" in my checking account. At the end of hte night, he'll only charge what I paid for and the release the other funds.
Let's say that my rent check attemps to clear the bank while they freeze in funds is on hold. If I only had $450 on my checking account, I could safely write a $400 check, which I did. But if hte bartender authorizes $75, my rent check will bounce because of NSF - even though I had that money in there!
This also holds true for things like RMAs when the funds are frozen for several weeks.
Bottom line is that check cards = bad. Don't even get me started on when your number gets stolen...