App lock is a waste of time and annoying. What I suggest is learning how to prevent people from getting in your phone in the first place. One step to doing that is encrypting your phone. I believe the newer phones already come encrypted but check to be sure. Another thing you can do is using fingerprint instead of a pin. This would prevent anyone from getting in, in the first place. I also highly recommend disabling unknown sources. That one option is the only thing that makes android unsecure (beside exploits). When you disable that it's just as vulnerable as a iphone.