Adguard can't be bad & i guess u enabled phishing site & malicious sites detection of adguard & google safe browsing under browser security category. Sure it will be miss malicious urls specially the new one since it's primary task is blocking ads not malicious urls but same way it will block too. I tested k9 & adguard combination few times already & adguard did blocked . If u allow some links which k9 blocked ,adguard will catch them coz K9 block faster then adguard, if K9 miss then it will caught by adguard. Also K9 is not good against latest phishing url but is good against other malicious url. Adguard blocked many infected urls which k9 missed in my test.