Any free parental control that is good enough?
Unfortunately, no. It is complete waste of time to even try them because at the end of day, you will have to give up and feeling so frustrated. If you are paying for a good app and are happy with it, I would suggest that you keep it. If you are looking for some very very basic control, you can try some built-in features of later versions of Android. Refer to the page below for some good information.
If you want anything more than that, you need to find a good paid solution.