Is a PIN lock screen inherently more or less secure than an app lock program?
You could always Encrypt your device. 

Depending on what phone you are using will determine the method or even availablity of this function.

It takes time though and you should do it with about 80-90% battery.

Also, I beleive the fact that your phone is rooted, makes it less secure - assuming the thief/person who picked up your phone (assuming that it was to be lost). 

As long as they can access the internal/external storage, they can bypass this.