This is safe, as long as you use this app to remove all traces of KingRoot once root is confirmed:
https://play.google.com/store/apps/details?id=darkslide.com.supersumepro
I've used KingRoot on several devices, then applied Super-Sume Pro. This is necessary if you want to run stock after rooting. If you can use custom recovery, and a custom ROM, that erases all traces of KingRoot from your device. Yes, I do know the dangers of leaving KingRoot on. Aside from it being possibly malware, it also eats up space for other apps it tries to push on your phone. SS Pro costs $4, but it's worth it if you use several devices to easily root, and want to retain a stock setup.