Keep in mind you're only liable for the first $50 in fraud on a credit card. In practice most US institutions will cover 100% of credit or electronic banking losses.
On the flip side, any SAAS that monitored your bank transactions would likely be more interested in developing and selling a profile of you than protecting you.
My idea was that the private,non-SAAS tool could track your total purchases on a particular category (food, gas, restaurants), or even a specific store, and inform you when you are blowing your budget. ("Hey, that latte put you over for the month. Better cut back").
On the flip side, any SAAS that monitored your bank transactions would likely be more interested in developing and selling a profile of you than protecting you.