I'm not particularly fond of the approach wherein you're required to provide your credit card details just to download an app. If you forget to cancel something, your card gets charged. This isn't an issue exclusive to Scannero; it applies to all apps. It seems like the Apple Store is encouraging us to spend more, even before we've decided whether we need a particular app or not.
I had the opportunity to test Scannero and I cancelled the subscription afterward. I believe that the option to test it for just a dollar is an excellent feature.